It is not uncommon for humans to find themselves with the intuition that random, unplanned, unexplained accident just couldn't produce the order, beauty, elegance, and seeming purpose that we experience in the natural world around us. As Hume's interlocutor Cleanthes put it, we seem to see “the image of mind reflected on us from innumerable objects” in nature. (Hume 1779 , 35). And many people find themselves convinced that no explanation for that mind-resonance which fails to acknowledge a causal role for intelligence, intent and purpose in nature can be seriously plausible.
Cosmological arguments begin with the bare fact that there are contingently existing things and end with conclusions concerning the existence of a cause with the power to account for the existence of those contingent things. Teleological arguments (or arguments from design) by contrast begin with a much more specialized catalogue of properties and end with a conclusion concerning the existence of a designer with the intellectual properties (knowledge, purpose, understanding, foresight, wisdom, intention) necessary to design the things exhibiting the special properties in question. In broad outline, then, teleological arguments focus upon finding and identifying various traces of the operation of a mind in nature's temporal and physical structures, behaviors and paths. Order of some significant type is usually the starting point of design arguments. Various advocates have focused on different types, levels and instances of order, have suggested different logical connections between order, design and designer and have pursued different levels of rigor—from Bayesian formalisms to the deadly serious whimsy of G.K. Chesterton:
So one elephant having a trunk was odd; but all elephants having trunks looked like a plot. (Chesterton 1908, 106–7)
Design-type arguments are largely unproblematic when based upon things nature clearly could not or would not produce (e.g., most human artifacts), or when the intelligent agency is itself ‘natural’ (human, alien, etc.). Identifying designed traces of ‘lost’ human civilizations or even non-human civilizations (Alpha Centaurian, say, via SETI) could in principle be uncontroversial or even nearly trivial. If we are confronted with something which nature unaided by an intelligence truly could not or would not produce (e.g., a DVD player), a design conclusion of some sort is very nearly inescapable. The uncontroversial nature of such inferences has often been appropriated as a foundation for analogous arguments concerning (things in) nature. But in cases involving design in (or of) nature itself inferences are more problematic, since the intelligence in question would presumably not be natural.
But despite the variety of spirited critical attacks they have elicited, design arguments have historically had and continue to have widespread intuitive appeal—indeed, it is sometimes claimed that design arguments are the most persuasive of all purely philosophical theistic arguments.
2. Design Inference Patterns
The historical arguments of interest are precisely the potentially problematic ones—inferences beginning with some empirical features of nature and concluding with the existence of a designer. A standard but separable second step—the natural theology step—involves identifying the designer as God, often via particular properties and powers required by the designing in question. Although the argument wielded its greatest intellectual influence during the 18th and early 19th centuries, it goes back at least to the Greeks and in extremely clipped form comprises one of Aquinas's Five Ways. It was given a fuller and quite nice early statement by Hume's interlocutor Cleanthes:
Look round the world; contemplate the whole and every part of it: You will find it to be nothing but one great machine, subdivided into an infinite number of lesser machines, which again admit of subdivisions to a degree beyond what human senses and faculties can trace and explain. All these various machines, and even their most minute parts, are adjusted to each other with an accuracy which ravishes into admiration all men who have ever contemplated them. The curious adapting of means to ends, throughout all nature, resembles exactly, though it much exceeds, the productions of human contrivance; of human design, thought, wisdom, and intelligence. Since, therefore, the effects resemble each other, we are led to infer, by all the rules of analogy, that the causes also resemble; and that the Author of Nature is somewhat similar to the mind of man, though possessed of much larger faculties, proportioned to the grandeur of the work which he has executed. By this argument a posteriori, and by this argument alone, do we prove at once the existence of a Deity, and his similarity to human mind and intelligence. (Hume 1779 , 15).
That statement captures much of popular, informal design intuitions, but exactly how ought we to construe the formal structure of such arguments? What sort of logic is being employed? As it turns out, that question does not have just a single answer. Several distinct answers are canvassed in the following sections.
2.1 Analogical Design Arguments: Schema 1
Design arguments are routinely classed as analogical arguments—various parallels between human artifacts and certain natural entities being taken as supporting parallel conclusions concerning operative causation in each case. (Note that Cleanthes, above, specifically appeals to “the rules of analogy.”) The standardly ascribed schema is roughly thus:
- Entity e within nature (or the cosmos, or nature itself) is like specified human artifact a (e.g., a machine) in relevant respects R.
- a has R precisely because it is a product of deliberate design by intelligent human agency.
- Like effects typically have like causes (or like explanations, like existence requirements, etc.)
- It is (highly) probable that e has R precisely because it too is a product of deliberate design by intelligent, relevantly human-like agency.
(The relevant respects and properties R are referred to variously as teleological properties or as marks or signs of design, and objects having such properties are sometimes referred to as teleological objects. For simplicity and uniformity of discussion, I shall simply talk in terms of “Rs”.)
2.1.1 Humean objections
This general argument form was criticized quite vigorously (and familiarly) by Hume, at several key steps. (Hume's primary critical discussion is contained in (Hume 1779 ). Hume's responses are widely taken as the paradigm philosophical refutation of traditional design arguments.) Against (1), Hume argued that the analogy is not very good—that nature and the various things in it are not very like human artifacts and exhibit substantial differences from them—e.g., living vs. not, self-sustaining vs. not. Indeed, whereas advocates of design arguments frequently cited similarities between the cosmos on the one hand and human machines on the other, Hume suggested (tongue perhaps only partly in cheek) that the cosmos much more closely resembled a living organism than a machine. But if the alleged resemblance is in relevant respects distant, then the inference in question will be logically fragile. And while (2) may be true in specific cases of human artifacts a, that fact is only made relevant to natural phenomena e via (3), which underpins the transfer of the key attribution. Against (3), Hume argued that any number of alternative possible explanations could be given of allegedly designed entities in nature—chance, for instance, or saturation of the relevant state space of possibilities. Thus, even were (1) true and even were there important resemblances, the argument might confer little probabilistic force onto the conclusion.
More generally, Hume also argued that even if something like the stated conclusion (4) were established, that left the arguer far from anything like a traditional conception of God. For instance, natural evils or apparently suboptimal designs might suggest e.g., an amateur designer or a committee of designers. And if phenomena instrumental to the production of natural evils (e.g., disease microorganisms) exhibited various of the Rs, then they would presumably have to be laid at the designer's door, further eroding the designer's resemblance to the wholly good deity of tradition. And even the most impressive empirical data could properly establish only finite (although perhaps enormous) power and wisdom, rather than the infinite power and wisdom usually associated with divinity. But even were one to concede some substance to the design arguments's conclusion, that would, Hume suggested, merely set up a regress. The designing agent would itself demand explanation, requiring ultimately a sequence of prior analogous intelligences producing intelligences. And even were the existence of a designer of material things established, that did not yet automatically establish the existence of a creator of the matter so shaped. And since analogical arguments are a type of induction (see the entry on analogy and analogical reasoning), the conclusion even if established would be established only to some, perhaps insignificant, degree of probability. Furthermore, we could not ground any induction concerning the cosmos itself upon a requisite fund of experiences of other cosmoi found to be both deliberately designed and very like ours in relevant respects—for the simple reason that this universe is our only sample. And finally the fraction of this one cosmos (both spatially and temporally) available to our inspection is extraordinarily small—not a promising basis for a cosmically general conclusion. Hume concluded that while the argument might constitute some limited grounds for thinking that “the cause or causes of order in the universe probably bear some remote analogy to human intelligence” (Hume 1779 , 88) Hume's emphasis)—and that is not a trivial implication—it established nothing else whatever.
Historically, not everyone agreed that Hume had fatally damaged the argument. For one thing, some of Hume's criticisms rested upon his own peculiar conception of causation—a conception nearly universally recognized as seriously inadequate. Further it is simply not true that explanatory inferences cannot properly extend beyond merely what is required for known effects. As a very general example, on the basis of the few observations which humans had made during a cosmically brief period in a spatially tiny part of the cosmos, Newton theorized that all bits of matter at all times and in all places attracted all other bits of matter. There was nothing whatever logically suspect here. Indeed, simplicity and uniformity considerations—which have considerable well-earned scientific clout—push in the direction of such generalizations.
But Hume certainly identified important places within the argument to probe. First, any two (groups of) things have infinitely many properties in common and also differ in infinitely many respects. Whether or not artifacts and natural objects are alike in ways that would support transfer of design attributions from the former to the latter depends upon exactly what the relevant Rs are. Second, whether or not there really are alternative means of producing Rs independent of any mind input is often an empirical matter, which cannot be settled either way by simple stipulation. On the other hand, whether or not some of Hume's own remarks are to the point depends upon whether or not design arguments really are ultimately analogical. And whether or not Hume's suggestions are correct concerning the uncertain character of any designer inferred will depend upon the specific Rs and upon what can or cannot be definitively said concerning requirements for their production.
2.1.2 R Concerns: Round 1
Key questions, then, include: what are the relevant Rs typically cited? do those Rs genuinely signal purpose and design? how does one show that either way? are there viable alternative accounts of the Rs requiring no reference to minds? how does one show that either way? The specific Rs in question are obviously central to design argument efforts. Although the underlying general category is, again, some special type of orderliness, the specifics have ranged rather widely historically. Among the more straightforwardly empirical are inter alia uniformity, contrivance, adjustment of means to ends, particularly exquisite complexity, particular types of functionality, delicacy, integration of natural laws, improbability, and the fitness (fine-tuning) of the inorganic realm for supporting life. A number of empirically further removed and problematic proposals all having axiological overtones have also been advanced, including the intelligibility of nature, the directionality of evolutionary processes, aesthetic characteristics (beauty, elegance, and the like), apparent purpose and value (including the aptness of our world for the existence and practice of moral value) and just the sheer niftiness of many of the things we find in nature.
Many of the specific Rs advanced historically were vulnerable to substantive critiques, often increasingly so as time went on. Specifically, while it was clearly evident that various a's had the R character they did in virtue of their (human) intentional production, it was much more difficult establishing that any or all other occurrences of R likely owed their existence to intention as well. As the standard story has it, science increasingly acquired understandings of how nature unaided by deliberate intent and planning could produce virtually any R proposed, and thus while (2) might continue to hold for virtually any human artifact a having any intended R one might please, (3) — and consequently the inference to (4) — became progressively less defensible. Design, on this telling, might gradually be explained away.
2.2 Deductive Design Arguments: Schema 2
But some advocates of design arguments had been reaching for a deeper intuition. The intuition they were attempting to capture involved properties that in and of themselves constituted some degree of evidence for design—properties that were not merely constantly conjoined, for whatever reason, with instances of design. The specific Rs were singled out not just because such properties happened to be often or even only produced by designing agents. (Garbage heaps fit that description.) Advocates were convinced that the appropriate Rs in question were in their own right directly reflective of and redolent of cognition, that this directly suggested mind, that we could see nearly directly that they were the general sort of thing that a mind might or even would generate, and that consequently they did not depend for their evidential force upon previously established constant conjunctions or other associations with known instances of design. When we see a text version of the Gettysburg Address, that text says mind to us in a way totally unrelated to any induction or analogy from past encounters with written texts. It was that type of testimony to mind, to design, that some historical advocates of design arguments believed that they found in some Rs observed in nature—a testimony having no dependency on induction or analogy. Beauty, purpose and in general value especially when conjoined with delicate complexity were popular underlying intuitive marks. Intricate, dynamic, stable, functioning order of the sort we encounter in nature was frequently placed in this category. Such order was taken to be suggestive of minds in that it seemed nearly self-evidently the sort of thing minds, and so far as was definitively known, only minds were prone to produce. It was a property whose mind-resonating character we could unhesitatingly attribute to intent.
Despite Hume's earlier demurs that things in nature are not really very like artifacts such as machines, most people (including opponents of design arguments) who are most familiar with nature's dazzling intricacies freely admit that nature abounds with things that look designed—that are intention-shaped. For instance, Francis Crick (no fan of design) issued a warning to his fellow biologists:
Biologists must constantly keep in mind that what they see was not designed, but rather evolved. (Crick 1988, 138).
Along with this perception of mind-suggestiveness went a further principle—that the mind-suggestive or intention-shaped (the design-like) characteristics in question were too palpable to have been generated by non-intentional means.
That allows specification of a second design inference pattern:
- Some things in nature (or nature itself, the cosmos) are design-like (exhibit a cognition-resonating, intention-shaped character R)
- Design-like properties (R) are not producible by (unguided) natural means—i.e., any phenomenon exhibiting such Rs must be a product of intentional design.
- Some things in nature (or nature itself, the cosmos) are products of intentional design. And of course, the capacity for intentional design requires agency of some type.
Notice that explicit reference to human artifacts has dropped out of the argument, and that the argument is no longer comparative but has become essentially deductive. Some arguments were historically intended as arguments of that type. Consider the widely reproduced opening passages of William Paley's 1802 Natural Theology:
In crossing a heath, suppose I pitched my foot against a stone and were asked how the stone came to be there, I might possibly answer that for anything I knew to the contrary it had lain there forever; nor would it, perhaps, be very easy to show the absurdity of this answer. But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place. I should hardly think of the answer which I had before given, that for anything I knew the watch might have always been there. Yet why should not this answer serve for the watch as well as for the stone? Why is it not as admissible in the second case as in the first? For this reason, and for no other, namely, that when we come to inspect the watch, we perceive—what we could not discover in the stone—that its several parts are framed and put together for a purpose … [The requisite] mechanism being observed … the inference we think is inevitable, that the watch must have had a maker. ... Every observation which was made in our first chapter concerning the watch may be repeated with strict propriety concerning the eye, concerning animals, concerning plants, concerning, indeed, all the organized parts of the works of nature. … [T]he eye … would be alone sufficient to support the conclusion which we draw from it, as to the necessity of an intelligent Creator. …
Although Paley's argument is routinely construed as analogical, it in fact contains an informal statement of the above variant argument type. Paley goes on for two chapters discussing the watch, discussing the properties in it which evince design, destroying potential objections to concluding design in the watch, and discussing what can and cannot be concluded about the watch's designer. It is only then that entities in nature—e.g., the eye—come onto the horizon at all. Obviously, Paley isn't making such heavy weather to persuade his readers to concede that the watch really is designed and has a designer. He is, in fact, teasing out the bases and procedures from and by which we should and should not reason about design and designers. Thus Paley's use of the term ‘inference’ in connection with the watch's designer.
Once having acquired the relevant principles, then in Chapter 3 of Natural Theology—“Application of the Argument”—Paley applies the same argument (vs. presenting us with the other half of the analogical argument) to things in nature. The cases of human artifacts and nature represent two separate inference instances:
up to the limit, the reasoning is as clear and certain in the one case as in the other. (Paley 1802 , 14)
But the instances are instances of the same inferential move:
there is precisely the same proof that the eye was made for vision as there is that the telescope was made for assisting it. (Paley 1802  13)
The watch does play an obvious and crucial role—but as a paradigmatic instance of design inferences rather than as the analogical foundation for an inferential comparison.
Schema 2, not being analogically structured, would not be vulnerable to the ills of analogy, and not being inductive would claim more than mere probability for its conclusion. That is not accidental. Indeed, it has been argued that Paley was aware of Hume's earlier attacks on analogical design arguments, and deliberately structured his argument to avoid the relevant pitfalls (Gillispie 1990, 214–229).
2.2.1 Assessing the Schema 2 argument
First, how are we to assess the premises required by this schema? Premise (5), at least, is not particularly controversial even now. Crick's earlier warning to biologists would have been pointless were there no temptation toward design attributions, and even as implacable a contemporary opponent of design arguments (and all things remotely related to them) as Richard Dawkins characterized biology as:
the study of complicated things that give the appearance of having been designed for a purpose. (Dawkins 1987, 1)
Day-to-day contemporary biology is rife with terms like ‘design’, ‘machine’, ‘purpose’ and allied terms. As historian of science Timothy Lenoir has remarked:
Teleological thinking has been steadfastly resisted by modern biology. And yet, in nearly every area of research biologists are hard pressed to find language that does not impute purposiveness to living forms. (Lenoir 1982, ix)
Whether or not particular biological phenomena are designed, they are frequently enough design-like to make design language (resisted or not) not only fit living systems extraordinarily well, but to undergird generation of fruitful theoretical conceptions as well. Advocates of design arguments claim that the reason why theorizing as if organisms are designed meets with such success is that organisms are in fact designed. Those opposed would say that all teleological concepts in biology must, in one way or another, be reduced to natural selection.
However principle (6) (that the relevant design-like properties are not producible by unguided natural means) will be more problematic in biology. (It will, of course, continue to play a role in fields such as archeology: what is a pottery shard vs. what is natural.) What might be the rational justification for (6)? There are two broad possibilities.
1. Empirical: induction. Induction essentially involves establishing that some principle holds within the realm of our knowledge/experience (the sample cases), and then, subject to certain constraints, generalizing the principle to encompass relevant areas beyond that realm (the test cases). The attempt to establish the universality of a connection between having relevant Rs and being a product of mind on the basis of an observed consistent connection between having relevant Rs and being a product of mind within all (most) of the cases where both R was exhibited and we knew whether or not the phenomenon in question was a product of mind, would constitute an inductive generalization.
This approach would suffer from a variety of weaknesses (some of them related to Hume's criticisms of Schema 1 arguments). The R-exhibiting things concerning which we knew whether or not they were designed would be almost without exception human artifacts, whereas the phenomena to which the generalization was being extended would be almost without exception things in a very different category—things in nature. And, of course, the generalization in question could establish at best a probability, and a fairly modest one at that.
2. Conceptual. It might be held that (6) is known in the same conceptual, nearly a priori way in which we know that textbooks are not producible by natural processes unaided by mind. And our conviction here is not based on any mere induction from prior experiences of texts. Texts carry with them essential marks of mind, and indeed in understanding a text we see at least partway into the mind(s) involved. Various alien artifacts (if any)—of which we have had no prior experience whatever—could fall into this category as well. Similarly, it has been held that we sometimes immediately recognize that order of the requisite sort just is a sign of mind and intent.
Alternatively, it could be argued that although there was a genuine conceptual link between appropriate Rs and mind, design, intent etc., that typically our recognition of that link is triggered by specific experiences with artifacts, or that our seeing the connections in depth is best elicited by considerations involving artifacts. (Both Aristotle and Galileo held a correlate of this view concerning our acquiring knowledge of the general principles governing nature.) On this view, once the truth of (6) became manifest to us through experiences of artifacts, the appropriateness of its more general application would be clear. That might explain why so many advocates of design arguments—both historical and current—seem to believe that they must only display a few cases and raise their eyebrows to gain assent to design.
Either way, principle (6), or something like it, would be something with which relevant design inferences would begin. Further investigation of (6) requires taking a closer look at the Rs which (6) involves.
2.2.2 R Concerns: Round 2
One thing complicating general assessments of design arguments is that the evidential force of specific Rs is affected by the context of their occurrence. Specifically, properties which seem clearly to constitute marks of design in known artifacts often seem to have significantly less evidential import outside that context. For instance, we typically construe enormous complexity in something known to be a manufactured artifact as a deliberately intended and produced characteristic. But mere complexity in contexts not taken to involve artifacts (the precise arrangement of pine needles on a forest floor, for instance) does not seem to have that same force. In the case of natural objects with evident artifactuality absent, it is less clear that such complexity—as well as the other traditional empirical Rs—bespeaks intention, plan and purpose. Similarly, absolutely straight lines in an artifact are typically results of deliberate intention. That straight lines traveled by light rays is so would seem to many to be less obvious.
Furthermore, even within those two contexts—artifact and nature—the various Rs exhibit varying degrees of evidential force. For instance, even in an artifact, mere complexity of whatever degree speaks less clearly of intent than does an engraved sentence. As most critics of design arguments point out, the examples found in nature are not of the “engraved sentence” sort.
There are two crucial upshots. First, notice that in general, the more empirically tractable the specific Rs, the less promising as marks of purpose and design they seem. For instance, if just bare complexity is cited, then although complexity is in many respects easily demonstrable, that complexity may not clearly speak of intent. On the other hand, although the exhibiting of genuine purpose and value might constitute persuasive and even compelling evidence of a designer, establishing that the empirical characteristics in question really do betoken genuine purpose and value—and not just, say, functionality—seems to many to be difficult if not impossible.
2.2.3 Gaps and Their Discontents
Evidential ambiguity would virtually disappear if it became clear that there is no plausible means of producing some R independent of deliberate intent. Part of the persuasiveness of (6) historically came from absence of any known plausible non-intentional alternative causal account of the traditional Rs. Such cases are often linked to alleged gaps in nature—phenomena for which, it is claimed, there can be no purely natural explanation, there being a gap between nature's production capabilities and the phenomenon in question. (For example, nature's unaided capabilities fall short of those capabilities required for producing a DVD player. Thus, when we see a DVD player we know that something else—human agency—was involved in its production.) Design cases resting upon nature's alleged inability to produce some relevant ‘natural’ phenomenon are generally assumed to explicitly or implicitly appeal to supernatural agency, and are typically described as “God-of-the-gaps” arguments—a description usually intended to be pejorative.
But evidence of design in nature does not automatically imply gaps. Design built or "front-loaded" into nature from the very beginning would require no further interventions within the historical flow of nature and therefore no gaps. But since the artifact/nature divide parallels the gap/non-gap divide, one way the implausibility of alternative means of production could become exceptionally clear was if R were associated with a gap in nature's capabilities—if the unaided course of nature genuinely could not or would not produce R, yet we see R in ‘nature’. In such a case, the appeal to agency would be virtually inevitable.
The position that there are gaps in nature is not inherently irrational—and would seem to be a legitimate empirical question. But although gaps would profoundly strengthen design arguments, they do import their own suite of difficulties. Gaps are usually easy to spot in cases of artifactuality, but although they may be present in nature, establishing their existence there can usually be done (by science, at least) only indirectly—via probability considerations, purported limitations on nature's abilities, etc.
Several possible snags lurk. Gaps in nature would, again, suggest supernatural agency, and some (for various reasons) take science to operate under an obligatory exclusion of such. This prohibition—commonly known as methodological naturalism—is often claimed (mistakenly, some argue) to be definitive of genuine science. ‘Established’ limitations both on science and on nature can and have been overturned in the past. The possibility of discovery (or postulation) of alternative ‘natural’ means of production would constitute a standing threat to any argument resting in part on a perceived absence of such means. And the spotty track record of alleged gaps provides at least a cautionary note. Such considerations will complicate attempts to very firmly establish design empirically on the basis of the types of properties we usually find in nature.
The way that alleged gaps typically disappear is, of course, through new proposed scientific theories postulating means of natural production of phenomena previously thought to be beyond nature's capabilities. The most obvious example of that is, of course, Darwin's evolutionary theory and its descendants. (That issue will resurface shortly.)
2.3 Inferences to the Best Explanation/Abductive Design Arguments: Schema 3
Some philosophers of science claim that in a wide variety of scientific cases we employ an “inference to the best explanation” (IBE). The basic idea is that if one among a number of competing candidate explanations is overall superior to others in significant respects — enhanced likelihood, explanatory power and scope, causal adequacy, plausibility, evidential support, fit with already-accepted theories, predictiveness, fruitfulness, precision, unifying power, and the like — then we are warranted in (provisionally) accepting that candidate as the right explanation given the evidence in question. Some advocates see design arguments as inferences to the best explanation, taking design explanations — whatever their weaknesses — as prima facie superior to chance, necessity, chance-driven evolution, or whatever.
Peter Lipton describes IBE this way (1991, 58):
According to Inference to the Best Explanation … [g]iven our data and our background beliefs, we infer what would if true, provide the best of the competing explanations we can generate of those data (so long as the best is good enough for us to make any inference at all).
Extracting a general schema from that description, and deploying it in the current case would give us the following:
- Some things in nature (or nature itself, the cosmos) exhibit exquisite complexity, delicate adjustment of means to ends (and other relevant R characteristics).
- The hypothesis that those characteristics are products of deliberate, intentional design (Design Hypothesis) would adequately explain them.
- In fact, the hypothesis that those characteristics are products of deliberate, intentional design (Design Hypothesis) is the best available overall explanation of them.
- Some things in nature (or nature itself, the cosmos) are products of deliberate, intentional design (i.e., the Design Hypothesis is likely true).
In arguments of this type, superior explanatory virtues of a theory are taken as constituting decisive epistemic support for theory acceptability, warranted belief of the theory, and likely truth of the theory. There are, of course, multitudes of purported explanatory, epistemic virtues, including the incomplete list a couple paragraphs back (and lists of such have evolved over time). Assessing hypotheses in terms of such virtues is frequently contentious, depending, as it does, on perceptions of ill-defined characteristics, differences in background conceptual stances, and the like. Still, in general we frequently manage rough and ready resolutions.
2.3.1 IBE, Likelihood and Bayes
One key underlying structure in this context is typically traced to Peirce's notion of abduction. Suppose that some otherwise surprising fact e would be a reasonably expectable occurrence were hypothesis h true. That, Peirce argued, would constitute at least some provisional reason for thinking that h might actually be true. Peirce's own characterization was as follows (Peirce 1955, 151):
- The surprising fact, C, is observed.
- But if A were true, C would be a matter of course.
- There is reason to suspect that A is true.
The measure of C being a ‘matter of course’ given A is frequently described as the degree to which C could be expected were A in fact true. This intuition is sometimes formalized in terms of likelihood, defined as follows:
The likelihood of hypothesis h (given evidence e) = P(e/h)
That the likelihood of h (given e) is high normally means that e being true or occurring constitutes some degree of support for h. In cases of competing explanatory hypotheses — say h1 and h2 — the comparative likelihoods on specified evidence can be taken to indicate which of the competitors specific pieces of evidence differentially support, i.e.:
[P(e/h1) > P(e/h2)] ⇔
(e supports h1 more strongly than it does h2)
Higher likelihood of h1 than h2 on specific evidence does not automatically imply that h1 should be accepted, is likely to be true, or is better in some overall sense than is h2. h1 might, in fact, be a completely lunatic theory which nonetheless entails e, giving h1 as high a likelihood as possible. Such maximal likelihood relative to e would not necessarily alter h1's lunacy. Likelihood thus does not automatically translate into a measure of how strongly some specific evidence e supports the hypothesis h1 in question.
This, then, leads directly to Bayesian probability theory. While the Bayesian approach is undoubtedly more rigorous than appeals to IBE, it is also somewhat of a digression, given that few teleological arguments are presented in these terms. For more on Bayesian epistemology and its problems, see the entry on epistemology-bayesian. For a contrast between IBE and Bayesianism, see abduction. For an important recent critique of theistic design arguments in Bayesian terms, see (Sober 2009) and the reply by (Kotzen 2012).
Whatever one's view of Bayesianism, IBEs have their own shortcomings. The assessment of ‘best’ is not only a value-tinged judgment, but is notoriously tricky (especially given the ambiguous and hard to pinpoint import of the Rs in the present case). There is also the very deep question of why we should think that features which we humans find attractive in proposed explanations should be thought to be truth-tracking. What sort of justification might be available here? Furthermore, taking design to be the best explanation for something requires prior identification of the appropriate properties as design-relevant, and that recognition must have a different basis. And again, substantive comparison can only involve known alternatives, which at any point represent a vanishingly small fraction of the possible alternatives. Choosing the best of the known may be the best we can do, but many (e.g., van Fraassen) would insist that without some further suppressed and significant assumptions, being the best (as humans see it) of the (humanly known) restricted group does not warrant ascription of truth, or anything like it.
There are other potential issues here as well. Sober argues that without additional very specific assumptions about the putative designer we could specify no particular value for P (e/h) — e.g., the likelihood that a designer would produce vertebrate eyes with the specific features we observe them to have — and that depending on the specific assumptions made we could come up with any value from 0 to 1 (e.g.Sober 2003, 38)
There is also the potential problem of new, previously unconsidered hypotheses all lumped together in the catch-all basket. Without knowing the details of what specific unconsidered hypotheses might look like, there is simply no plausible way to anticipate the apparent likelihood of a novel new hypothesis — let alone its other potential explanatory virtues. This, on some views, is essentially what happened with traditional design arguments — such arguments were the most reasonable available until Darwinian evolution provided a plausible (or better) alternative the details and likelihood of which were not previously anticipatable.
3. Alternative Explanation
Without going into the very familiar details, Darwinian processes fueled by undesigned, unplanned, chance variations that are in turn conserved or eliminated by way of natural selection would, it is argued, over time produce organisms exquisitely adapted to their environmental niches. And since many of the characteristics traditionally cited as evidences of design just were various adaptations, evolution would thus produce entities exactly fitting traditional criteria of design. Natural selection, then, unaided by intention or intervention could account for the existence of many (perhaps all) of the Rs which we in fact find in nature. (A parallel set of arguments can be found between those who believe that life itself requires a design explanation (Meyer 2009) and those proposing naturalistic explanations (see the entry on life.)
That was—and is—widely taken as meaning that design arguments depending upon specific biological gaps would be weakened—perhaps fatally. Thus Darwin in a very famous passage from his autobiography:
The old argument of design in nature, as given by Paley, which formerly seemed to me so conclusive, fails, now that the law of natural selection had been discovered. We can no longer argue that, for instance, the beautiful hinge of a bivalve shell must have been made by an intelligent being, like the hinge of a door by man. There seems to be no more design in the variability of organic beings and in the action of natural selection, than in the course which the wind blows. Everything in nature is the result of fixed laws. (Darwin 1887, 279)
Premise (10) — not to mention the earlier (6) — would thus look to simply be false. What had earlier appeared to be purpose (requiring intent) was now apparently revealed as mere unintended but successful and preserved function.
Of course, relevant premises being false merely undercuts the relevant schemas in present form — it does not necessarily refute either the basic design intuition or other forms of design arguments. But some critics take a much stronger line here. Richard Dawkins, for instance, subtitles one of his books: “Why the evidence of evolution reveals a universe without design” (Dawkins, 1987). Typically underlying claims of this sort is the belief that Darwinian evolution, by providing a relevant account of the origin and development of adaptation, diversity, and the like, has explained away the alleged design in the biological realm — and an attendant designer — in much the same way that kinetic theory has explained away caloric. Indeed, this is a dominant idea underlying current responses to design arguments. However, undercutting and explaining away are not necessarily the same thing, and exactly what explaining away might mean, and what a successful explaining away might require are typically not clearly specified. So before continuing, we need clarity concerning some relevant conceptual landscape.
3.1 Explaining Away
That an alleged explanatory factor α is provisionally explained away requires that there be an alternative explanation Σ meeting these conditions:
- Σ is explanatorily adequate to the relevant phenomenon (structure, property, entity, event)
- Σ can be rationally supported in terms of available (or likely) evidence
- Σ is relevantly superior to the original in terms either of adequacy or support
- Σ requires no essential reference to α
However, (a) – (d) are incomplete in a way directly relevant to the present discussion. Here is a very simple case. Suppose that an elderly uncle dies in suspicious circumstances, and a number of the relatives believe that the correct explanation is the direct agency of a niece who is primary heir, via deliberately and directly administering poison. However, forensic investigation establishes that the cause of death was a mix-up among medications the uncle was taking — an unfortunate confusion. The suspicious relatives, however, without missing an explanatory beat shift the niece's agency back one level, proposing that the mix-up itself was orchestrated by the niece — switching contents of prescription bottles, no doubt. And that might very well turn out to be the truth.
In that sort of case, the α in question (e.g., niecely agency) is no longer directly appealed to in the relevant initial explanatory level, but is not removed from all explanatory relevance to the phenomenon in question. In general, then, for α to be explained away in the sense of banished from all explanatory relevance the following condition must also be met:
- no reference to α is required at any explanatory level underlying Σ
By that I mean roughly that Σ does not depend essentially on any part β of any prior explanation where α is essential to β. There are some additional possible technical qualifications required, but the general intuition should be clear.
Thus, e.g., whereas there was no need to appeal to caloric at some prior or deeper level, with design, according to various design advocates, there is still an explanatory lacuna (or implicit promissory note) requiring reference to design at some explanatory level prior to Darwinian evolution. Indeed, as some see it (and as Paley himself suggested), there are phenomena requiring explanation in design terms which cannot be explained away at any prior explanatory level (short of the ultimate level).
That some phenomenon α has been explained away can be taken to mean two very different things — either as
- showing that it is no longer rational to believe that α exists
- showing that α does not exist
(And often, of course, both.)
For instance, few would assert that there is still an extant rational case for belief in phlogiston — any explanatory work it did at the proximate level seems to have ceased, and deeper explanatory uses for it have never subsequently materialized. Perhaps its non-existence was not positively established immediately, but removal of rational justification for belief in some entity can morph into a case for non-existence as the evidence for a rival hypothesis increases over time
Purported explanations can be informally divided into two broad categories — those involving agents, agency, intention, and the like; and those involving mechanism, physical causality, natural processes, and the like. The distinction is not, of course, a clean one (functioning artifacts typically involve both), but is useful enough in a rough and ready way, and in what follows I will use agent explanations and mechanical explanations respectively as convenient handles. Nothing pernicious is built into either the broad distinction or the specified terminology.
There are some instructive patterns that emerge in explanatory level-shifting attempts, and in what immediately follows some of the more basic patterns will be identified.
(a) Agent explanations
Intention, intervention, and other agency components of explanations can very frequently be pushed back to prior levels — much as many defenders of teleological arguments claim. The earlier case of the alleged poisoning of the rich uncle by the niece is a simple example of this.
But in some cases, the specifics of the agent explanation in question may make appeal to some prior level less plausible or sensible. For example, suppose that one held the view that crop circles were to be explained in terms of direct alien activity. One could, upon getting irrefutable video proof of human production of crop circles, still maintain that aliens were from a distance controlling the brains of the humans in question, and that thus the responsibility for crop circles did still lie with alien activity. While this retreat of levels preserves the basic explanation, it of course comes with a significant cost in inherent implausibility.
And in some cases, pushing specific agency back a level seems nearly unworkable. Suppose that the standard explanation of global warming was human activity, but that subsequently a complete, completely adequate, nailed down explanation in terms of solar cycles emerged. That would seem to explain away the alleged human causation, and in this sort of case it would be difficult to retreat back one level and make the case that human agency and activity were actually driving the solar cycles.
Still the level-changing possibility is as a general rule available with proposed agent explanations. And design typically is, of course, an agent explanation.
(b) Mechanical explanations
Pushing specific explanatory factors back to a prior level often works less smoothly in cases of purely mechanical/physical explanations than in intentional/agency explanations. In many attempted mechanistic relocation cases, it is difficult to see how the specific relocated explanatory factor is even supposed to work, much less generate any new explanatory traction. Exactly what would caloric do if pushed back one level, for instance?
Although level shifting of specific explanatory factors seems to work less easily within purely physical explanations, relocation attempts involving broad physical principles can sometimes avoid such difficulties. For instance, for centuries determinism was a basic background component of scientific explanations (apparently stochastic processes being explained away epistemically). Then, early in the 20th century physics was largely converted to a quantum mechanical picture of nature as involving an irreducible indeterminism at a fundamental level — apparently deterministic phenomena now being what was explained away. However, DeBroglie, Bohm and others (even for a time Einstein) tried to reinstate determinism by moving it back to an even deeper fundamental level via hidden variable theories. Although the hidden variable attempt is generally thought not to be successful, its failure is not a failure of principle.
3.1.2 Possible disputes
How one assesses the legitimacy, plausibility, or likelihood of the specific counter-explanation will bear substantial weight here, and that in turn will depend significantly on among other things background beliefs, commitments, metaphysical dispositions, and the like. If one has a prior commitment to some key α (e.g., to theism, atheism, naturalism determinism, materialism, teleology), or assigns a high prior to that α, the plausibility of taking the proposed (new) explanation as undercutting, defeating, or refuting α (and/or Σ) will be deeply affected, at least initially.
Tilting the conceptual landscape via prior commitments is both an equal opportunity epistemic necessity and a potential pitfall here. Insisting on pushing an explanatory factor back a level is often an indication of a strong prior commitment of some sort. Disagreement over deeper philosophical or other principles will frequently generate divergence over when something has or has not been explained away. One side, committed to the principle, will accept a level change as embodying a deeper insight into the relevant phenomenon. The other, rejecting the principle, will see an ad hoc retreat to defend an α which has in fact been explained away.
Returning to the present issue, design argument advocates will of course reject the claim that design, teleology, agency and the like have been explained away either by science generally or by Darwinian evolution in particular. Reasons will vary. Some will see any science — Darwinian evolution included — as incompetent to say anything of ultimate design relevance, pro or con. (Many on both sides of the design issue fit here.) Some will see Darwinian evolution as failing condition (a), (b) and/or (c), claiming that Darwinian evolution is not explanatorily adequate to selected α's, is inadequately supported by the evidence, and is far from superior to agency explanations of relevant phenomena. (Creationists and some — not all — ‘intelligent design’ advocates fit here.) Some will argue that a Darwinian failure occurs at (d), citing e.g., a concept of information claimed to be both essential to evolution and freighted with agency. (Some intelligent design advocates fit here. (Dembski, 2002, Meyer, 1998) However, the major contention of present interest involves (e).
3.3 Indirect Causation, Design and Evidences
Historically, design cases were in fact widely understood to allow for indirect intelligent agent design and causation, the very causal structures producing the relevant phenomena being themselves deliberately designed for the purpose of producing those phenomena. For instance, it was typically believed that God could have initiated special conditions and processes at the instant of creation which operating entirely on their own could produce organisms and other intended (and designed) results with no subsequent agent intervention required. Paley himself, the authors of the Bridgewater Treatises and others (including even Augustine, earlier) were explicitly clear that whether or not something was designed was an issue largely separable from the means of production in question. Historically it was insisted that design in nature did track back eventually to intelligent agency somewhere and that any design we find in nature would not—and could not—have been there had there ultimately been no mind involved. But commentators (including many scientists) at least from the early 17th century on (e.g., Francis Bacon, Robert Boyle) very clearly distinguished the creative initiating of nature itself from interventions within the path of nature once initiated. For instance, over two centuries before Darwin, Bacon wrote:
God … doth accomplish and fulfill his divine will [by ways] not immediate and direct, but by compass; not violating Nature, which is his own law upon the creation. (quoted in (Whewell 1834, 358)
Indeed, if the Rs in question did directly indicate the influence of a mind, then means of production—whether unbroken causation or gappy—would be of minimal evidential importance. Thus, the frequent contemporary claim that design arguments all involve appeal to special divine intervention during the course of nature's history—that in short design arguments are “God-of-the-gaps” arguments—represents serious historical (and present) inaccuracy(e.g., Behe, 1996).
In fact, a decided preference for design cases not involving gaps and supernatural intervention was common long before Darwin. A quarter century prior to the Origin, Charles Babbage expressed a typical position:
We cannot for a moment hesitate in pronouncing that that which, after its original adjustment, no superintendence was required, displayed far greater ingenuity than that which demanded, at every change in its law, the intervention of its contriver. (Babbage 1838, 40)
Boyle had expressed the same idea as far back as the 1680s, and Whewell and others expressed related sentiments in the 1830s. This popular conception was neatly summarized by Mother Cary in Charles Kingsley's Water Babies:
[A]nyone can make things, if they will take time and trouble enough, but it is not everyone who, like me, can make things make themselves (Kingsley 1890, 273)
Indeed, even Darwin himself endorsed this view—a relevant quote from Whewell appears in the frontispiece of the Origin itself (Darwin 1859 , ii) —and he expressed related sentiments in his own words both in his pre-Origin notebooks and in his personal correspondence even after publication of the Origin. This sort of pre-Darwin move (relocating design from intervention back one level to created laws and deliberately chosen initial conditions) was thus obviously not just a forced retreat from Darwin, as frequently claimed.
However, if Rs result from gapless chains of natural causal processes, the evidential impact of those Rs again threatens to become problematic and ambiguous, since there will a fortiori be at the immediate level a full natural causal account for them. Design will, in such cases, play no immediate mechanistic explanatory role, suggesting its superfluousness. But even if such conceptions were explanatorily and scientifically superfluous at that level, that does not entail that they are conceptually, alethically, inferential, or otherwise superfluous in general. The role of mind might be indirect, deeply buried, or at several levels of remove from the immediate production mechanism but would still have to be present at some level. In short, on the above picture Darwinian evolution will not meet condition (e) for explaining away design. That is of course not a shortcoming of Darwinian evolution — unless one hopes to deploy Darwinian evolution as a weapon against design arguments (or, more broadly) theism.
But any gap-free argument will depend crucially upon the Rs in question being ultimately dependent for their eventual occurrence upon agent activity. That issue could be integrated back into an altered Schema 2 by replacing (6) with:
(6a) Design-like properties (R) are (most probably) not producible by means ultimately devoid of mind/intention—i.e., any phenomena exhibiting such Rs must be a product (at least indirectly) of intentional design.
The focus must now become whether or not the laws and conditions required for the indirect production of life, intelligent life, etc., could themselves be independent of intention, design and mind at some deep (perhaps primordial, pre-cosmic) point. In recent decades, exactly that question has arisen increasingly insistently from within the scientific community.
4. Further Contemporary Design Discussions
4.1 Cosmological: Fine-tuning
Intuitively, if the laws of physics were different, the evolution of life would not have taken the same path. If gravity were stronger, for example, then flying insects and giraffes would most likely not exist. The truth is far more dramatic. Even an extraordinarily small change in one of many key parameters in the laws of physics would have made life impossible anywhere in the universe. Consider two examples:
The expansion rate of the universe is represented by the cosmological constant Λ. If Λ were slighter greater, there would be no energy sources, such as stars. If it were slightly less, the Big Bang would have quickly led to a Big Crunch in which the universe collapsed back onto itself. For life to be possible, Λ cannot vary more than one part in 1053 (Collins 2003)
Life depends on, among other things, a balance of carbon and oxygen in the universe. If the strong nuclear force were different by 0.4%, there would not be enough of one or the other for life to exist (Oberhummer, Csótó, and Schlattl 2000). Varying this constant either way “would destroy almost all carbon or almost all oxygen in every star” (Barrow 2002, 155).
Many examples of fine-tuning have to do with star formation. Stars are important since life requires a variety of elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Stars contain the only known mechanism for producing large quantities of these elements and are therefore necessary for life. Lee Smolin estimates that when all of the fine-tuning examples are considered, the chance of stars existing in the universe is 1 in 10229. “In my opinion, a probability this tiny is not something we can let go unexplained. Luck will certainly not do here; we need some rational explanation of how something this unlikely turned out to be the case” (Smolin 1999, 45).
Most physicists agree with Smolin that the discovery of fine-tuning cries out for an explanation. One explanation is that the universe appears to be fine-tuned for the existence of life because it literally has been constructed for life by an intelligent agent.
There are two other types of responses to fine-tuning: (i) it does not, in fact, require a special explanation, and (ii) there are alternative explanations to theistic design. Let’s briefly consider these.
4.1.1 No explanation needed
Three approaches have been taken to undermine the demand for explanation presented by fine-tuning.
220.127.116.11 Weak anthropic principle
In a sense, it is necessary for the fine-tuned constants to have values in the life-permitting range: If those values were not within that range, people would not exist. The fine-tuned constants must take on the values that they have in order for scientists to be surprised by their discovery in the first place. As a matter of fact, they could not have discovered anything else. According to the weak anthropic principle, we ought not be surprised by having made such a discovery, since no other observation was possible. But if we should not have been surprised to have made such a discovery, then there is nothing unusual here that requires a special explanation. The demand for explanation is simply misplaced.
18.104.22.168 Observational selection effect
Sober gives a related but stronger argument based on observational selection effects (Sober 2009, 77–80). Say that Jones nets a large number of fish from a local lake, all of which are over 10 inches long. Let hall= ‘all of the fish in the lake are over 10 inches long’ and h1/2= ‘Half of the fish in the lake are over 10 inches long’. The evidence e is such that Pr(e|hall) > Pr(e|h1/2). Now say that Jones discovers that his net is covered with 10 inch holes, preventing him from capturing any smaller fish. In that case, e does not favor one hypothesis over the other. The evidence e is an artifact of the net itself, not a random sample of the fish in the lake.
When it comes to fine-tuning, Sober considers hdesign=‘the constants have been set in place by an intelligence, specifically God’, and hchance=‘the constants are what they are as a matter of mindless random chance’. While intuitively
Pr(constants are just right for life| hdesign) > Pr(constants are just right for life| hchance)
one has to consider the role of the observer, who is analogous to the net in the fishing example. Since human observers could only detect constants in the life-permitting range, Sober argues, the correct probabilities are
Pr(you observe that the constants are right| hdesign & you exist) = Pr(you observe that the constants are right| hchance & you exist).
Given this equality, fine-tuning does not favor hdesign over hchance. The selection effect prevents any confirmation of design.
Sober’s analysis is critiqued in (Monton 2006) and (Kotzen 2012). We should note that if Sober is correct, then the naturalistic explanations for fine-tuning considered below (4.1.2) are likewise misguided.
22.214.171.124 Probabilities do not apply
Let C stand for a fine-tuned parameter with physically possible values in the range . If we assume that nature is not biased toward one value of C rather than another, then each unit subinterval in this range should be assigned equal probability. Fine-tuning is surprising insofar as the life-permitting range of C is tiny compared to the full interval, which corresponds to a very small probability.
As McGrew, McGrew, and Vestrup argue (2001), there is a problem here in that, strictly speaking, mathematical probabilities do not apply in these circumstances. When a probability distribution is defined over a space of possible outcomes, it must add up to exactly 1. But for any uniform distribution over an infinitely large space, the sum of the probabilities will grow arbitrarily large as each unit interval is added up. Since the range of C is infinite, McGrew et al. conclude that there is no sense in which life-friendly universes are improbable; the probabilities are mathematically undefined.
One solution to this problem is to truncate the interval of possible values. Instead of allowing C to range from [0,∞), one could form a finite interval [0,N], where N is very large relative to the life-permitting range of C. A probability distribution could then be defined over the truncated range.
A more rigorous solution employs measure theory. Measure is sometimes used in physics as a surrogate for probability. For example, there are many more irrational numbers than rational ones. In measure theoretic terms, almost all real numbers are irrational, where “almost all” means all but a set of zero measure. In physics, a property found for almost all of the solutions to an equation requires no explanation; it’s what one should expect. It’s not unusual, for instance, for a pin balancing on its tip to fall over. Falling over is to be expected. In contrast, if a property that has zero measure in the relevant space were actually observed to be the case, like the pin continuing to balance on its tip, that would demand a special explanation. Assuming one’s model for the system is correct, nature appears to be strongly biased against such behavior (Gibbons, Hawking, and Stewart 1987, 736). The argument for fine-tuning can thus be recast such that almost all values of C are outside of the life-permitting range. The fact that our universe is life-permitting is therefore in need of explanation.
The question of whether probabilities either do not apply or have been improperly applied to cosmological fine-tuning continues to draw interest. For more, see (Davies 1992), (Callender 2004), (Holder 2004), (Koperski 2005), (Manson 2009), and (Koperski 2015, chap 2).
4.1.2 Rival explanations
Assuming that fine-tuning requires an explanation, there are several approaches one might take (Koperski 2015, section 2.4).
126.96.36.199 Scientific progress
That the universe is fine-tuned for life is based on current science. But, just as many other anomalies have eventually been explained, so might fine-tuning. Science may one day find a naturalistic answer, eliminating the need for design. For suggestions along these lines, see (Harnik, Kribs, and Perez 2006), Page 2011 (Other Internet Resources)), and (Loeb 2014).
While this is a popular stance, it is, of course, a promissory note rather than an explanation. The appeal to what might yet be discovered is not itself a rival hypothesis.
188.8.131.52 Exotic life
It’s conceivable that life could exist in a universe with parameter values that we do not typically believe are life-permitting. In other words, there may be exotic forms of life that could survive in a very different sort of universe. If so, then perhaps the parameter intervals that are in fact life-permitting are not fine-tuned after all.
The main difficulty with this suggestion is that all life requires a means for overcoming the second law of thermodynamics. Life requires the extraction of energy from the environment. Any life-form imaginable must therefore have systems that allow for something like metabolism and respiration, which in turn require a minimal amount of complexity (e.g., there can be no single-molecule life forms). Many examples of fine-tuning do not allow for such complexity, however. If there were no stars, for example, then there would be no stable sources of energy and no mechanism for producing the heavier elements in the periodic table. Such a universe would lack the chemical building blocks needed for a living entity to extract energy from the environment and thereby resist the pull of entropy.
While the odds of winning a national lottery are low, your odds would obviously increase if you were to buy several million tickets. The same idea applies to the most popular explanation for fine-tuning: a multiverse. Perhaps physical reality consists of a massive array of universes each with a different set of values for the relevant constants. If there are many—perhaps infinitely many—universes, then the odds of a life-permitting universe being produced would seem to be much greater. While most of the universes in the multiverse would be unfit for life, so the argument goes, ours is one of the few where all of the constants have the required values.
While the philosophical literature on the multiverse continues to grow (see (Collins 2009, 2012) and (Kraay 2014)), many of the arguments against it share a common premise: a multiverse would not, by itself, be a sufficient explanation of fine-tuning. More would have to be known about the way in which universes are produced. By analogy, just because a roulette wheel has 38 spaces does not guarantee that the probability of Red 25 is 1/38. If the wheel is rigged in some way—by using magnets for example—to prevent that outcome, then the probability might be extremely small. If the table were rigged and yet Red 25 was the actual winner, that would require a special explanation. Likewise, if a property has zero measure in the space of possible universes, and yet that property is observed, its existence would still require an explanation (Earman 1987, 315). This is true regardless of whether the space of universes is finitely or infinitely large. In order to explain fine-tuning, the multiverse proponent would still have to show that the life-permitting universes do not have zero measure in the space of all universes (Koperski 2005, 307–309).
4.2 Biological: The “Intelligent Design” Movement
A high-profile development in design arguments over the past 15 years or so involves what has come to be known as the “Intelligent Design” (ID) movement. Although there are variants, the movement involves efforts to construct design arguments taking cognizance of various contemporary scientific developments (primarily in biology, biochemistry, mathematics and cosmology)—developments which, as most ID advocates see it, both reveal the inadequacy of mainstream (naturalistic Darwinian) explanatory accounts (condition (a)) and offer compelling evidence for design in nature at some level (condition (e) again).
ID advocates propose three specialized Rs—irreducible complexity (Behe 1996), specified complexity and information (Dembski 1998, 2002). Although distinctions are sometimes blurred here, while ID arguments involving each of those Rs tend to be gap arguments, an additional focus on mind-reflective aspects of nature is typically more visible in ID arguments citing specified complexity and information than in arguments citing irreducible complexity.
The movement has elicited vociferous criticism and opposition. Opponents have pressed a number of objections against ID including, inter alia contentions that ID advocates have simply gotten the relevant science wrong, that even where the science is right the empirical evidences cited by design advocates do not, in fact, constitute substantive grounds for design conclusions, that the existence of demonstrably superior alternative explanations for the phenomena cited undercuts the cogency of ID cases, and that design theories are not legitimate science, but are just disguised creationism, God-of-the-gaps arguments, religiously motivated, etc.
We will not pursue that dispute here except to note that even if the case is made that ID could not count as proper science, which is controversial, that would not in itself demonstrate a defect in design arguments as such. Science need not be seen as exhausting the space of legitimate conclusions from empirical data. In any case, the floods of vitriol in the current ID discussion suggest that much more than the propriety of selected inferences from particular empirical evidences is at issue.
5. The Persistence of Design Thinking
That question is: why do design arguments remain so durable if empirical evidence is inferentially ambiguous, the arguments logically controversial, and the conclusions vociferously disputed? One possibility is that they really are better arguments than most philosophical critics concede. Another possibility is that design intuitions do not rest upon inferences at all. The situation may parallel that of the existence of an external world, the existence of other minds, and a number of other familiar matters. The 18th century Scottish Common Sense philosopher Thomas Reid (and his contemporary followers) argued that we are simply so constructed that in certain normally-realized experiential circumstances we simply find that we in fact have involuntary convictions about such a world, about other minds, and so forth. That would explain why historical philosophical attempts to reconstruct the arguments by which such beliefs either arose or were justified were such notorious failures—failures in the face of which ordinary belief nonetheless proceeded happily and helplessly onward. If a similar involuntary belief-producing mechanism operated with respect to intuitions of design, that would similarly explain why argumentative attempts have been less than universally compelling but yet why design ideas fail to disappear despite the purported failure of such arguments
A number of prominent figures historically in fact held that we could determine more or less perceptually that various things in nature were candidates for design attributions—that they were in the requisite respects design-like. Some, like William Whewell, held that we could perceptually identify some things as more than mere candidates for design (Whewell 1834, 344). Thomas Reid also held a view in this region, and Hume's Cleanthes made suggestions in this direction.
If something like that were the operative process, then the ID movement, in trying to forge a scientific link to design in the sense of inferences from empirically determined evidences would be misconstructing the actual basis for design belief, as would be design arguments more generally. It is perhaps telling, in this regard, that scientific theorizing typically involves substantial creativity and that the resultant theories are typically novel and unexpected. Design intuitions, however, do not seem to emerge as novel construals from creative grappling with data, but are embedded in our thinking nearly naturally—so much so that, again, Crick thinks that biologists have to be immunized against it. Indeed, design structures seem to be part of the very fabric of science itself. According to physicist Paul Davies
Science began as an outgrowth of theology, and all scientists, whether atheists or theists … accept an essentially theological worldview. (Davies 1995, 138)
All of that suggests to some that we are dealing with a different category of belief formation and acquisition. And it also suggests that design thinking may be natural to our sorts of intellects.
Perception and appreciation of the incredible intricacy and the beauty of things in nature—whether biological or cosmic—has certainly inclined many toward thoughts of purpose and design in nature, and has constituted important moments of affirmation for those who already accept design positions. The status of the corresponding arguments of course, is not only a matter of current dispute, but the temperature of the dispute seems to be on the rise. And regardless of what one thinks of the arguments at this point, so long as nature has the power to move us (as even Kant admitted that the ‘starry heavens above’ did), design convictions and arguments are unlikely to disappear quietly.
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- Manson, Neil (ed.), 2003. God and Design: The teleological argument and modern science, New York: Routledge.
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- –––, 2009. Signature in the Cell: DNA and the Evidence for Intelligent Design, New York: HarperOne.
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- Rott, Hans, 2010. “Idealizations, Intertheory Explanations and Conditionals,” in Belief Revision Meets Philosophy of Science (Logic, Epistemology, and the Unity of Science, Volume 21), edited by E. J. Olsson and S. Enqvist, 59–76, New York: Springer.
- –––, 2003. “Perceiving Design,” in Manson 2003, pp. 124–144.
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Other Internet Resources
- Page, Don N., 2011. “Preliminary Inconclusive Hint of Evidence Against Optimal Fine Tuning of the Cosmological Constant for Maximizing the Fraction of Baryons Becoming Life,” manuscript in arXiv.org.
- Natural Theology; or, Evidences of the Existence and Attributes of the Deity, by William Paley.
- Design Arguments for the Existence of God, by Kenneth Einar Himma (Seattle Pacific University), hosted by the Internet Encyclopedia of Philosophy.
- The Teleological Argument and the Anthropic Principle, by William Lane Craig (Talbot School of Theology), hosted by Leadership U.
- Anthropic-Principle.com, maintained by Nick Bostrom (Oxford University).
- Robin Collins's Fine-Tuning Website, maintained by Robin Collins (Messiah College).
Del Ratzsch would like to thank his colleagues in the Calvin College Philosophy Department, especially Ruth Groenhout, Kelly Clark and Terrence Cuneo, and to David van Baak.
Jeffrey Koperski would like to thank Hans Halvorson, Rodney Holder, and Thomas Tracy for helpful comments on source material for section 4.
Design Arguments for the Existence of God
Design arguments are empirical arguments for the existence of God. These arguments typically, though not always, proceed by attempting to identify various empirical features of the world that constitute evidence of intelligent design and inferring God's existence as the best explanation for these features. Since the concepts of design and purpose are closely related, design arguments are also known as teleological arguments, which incorporates "telos," the Greek word for "goal" or "purpose."
Design arguments typically consist of (1) a premise that asserts that the material universe exhibits some empirical property F; (2) a premise (or sub-argument) that asserts (or concludes) that F is persuasive evidence of intelligent design or purpose; and (3) a premise (or sub-argument) that asserts (or concludes) that the best or most probable explanation for the fact that the material universe exhibits F is that there exists an intelligent designer who intentionally brought it about that the material universe exists and exhibits F.
There are a number of classic and contemporary versions of the argument from design. This article will cover seven different ones. Among the classical versions are: (1) the "Fifth Way" of St. Thomas Aquinas; (2) the argument from simple analogy; (3) Paley's watchmaker argument; and (4) the argument from guided evolution. The more contemporary versions include: (5) the argument from irreducible biochemical complexity; (6) the argument from biological information; and (7) the fine-tuning argument.
Table of Contents
- The Classical Versions of the Design Argument
- Scriptural Roots and Aquinas's Fifth Way
- The Argument from Simple Analogy
- Paley's Watchmaker Argument
- Guided Evolution
- Contemporary Versions of the Design Argument
- The Argument from Irreducible Biochemical Complexity
- The Argument from Biological Information
- The Fine-Tuning Arguments
- The Argument from Suspicious Improbability
- The Confirmatory Argument
- The Scientifically Legitimate Uses of Design Inferences
- References and Further Reading
1. The Classical Versions of the Design Argument
a. Scriptural Roots and Aquinas's Fifth Way
The scriptures of each of the major classically theistic religions contain language that suggests that there is evidence of divine design in the world. Psalms 19:1 of the Old Testament, scripture to both Judaism and Christianity, states that "The heavens declare the glory of God; and the firmament sheweth his handywork." Similarly, Romans 1:19-21 of the New Testament states:
For what can be known about God is plain to them, because God has shown it to them. Ever since the creation of the world his eternal power and divine nature, invisible though they are, have been understood and seen through the things he has made. So they are without excuse.
Further, Koran 31:20 asks "Do you not see that Allah has made what is in the heavens and what is in the earth subservient to you, and made complete to you His favors outwardly and inwardly?" While these verses do not specifically indicate which properties or features of the world are evidence of God's intelligent nature, each presupposes that the world exhibits such features and that they are readily discernable to a reasonably conscientious agent.
Perhaps the earliest philosophically rigorous version of the design argument owes to St. Thomas Aquinas. According to Aquinas's Fifth Way:
We see that things which lack knowledge, such as natural bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way, so as to obtain the best result. Hence it is plain that they achieve their end, not fortuitously, but designedly. Now whatever lacks knowledge cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is directed by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God (Aquinas, Summa Theologica, Article 3, Question 2).
It is worth noting that Aquinas's version of the argument relies on a very strong claim about the explanation for ends and processes: the existence of any end-directed system or process can be explained, as a logical matter, only by the existence of an intelligent being who directs that system or process towards its end. Since the operations of all natural bodies, on Aquinas's view, are directed towards some specific end that conduces to, at the very least, the preservation of the object, these operations can be explained only by the existence of an intelligent being. Accordingly, the empirical fact that the operations of natural objects are directed towards ends shows that an intelligent Deity exists.
This crucial claim, however, seems to be refuted by the mere possibility of an evolutionary explanation. If a Darwinian explanation is even coherent (that is, non-contradictory, as opposed to true), then it provides a logically possible explanation for how the end-directedness of the operations of living beings in this world might have come about. According to this explanation, such operations evolve through a process by which random genetic mutations are naturally selected for their adaptive value; organisms that have evolved some system that performs a fitness-enhancing operation are more likely to survive and leave offspring, other things being equal, than organisms that have not evolved such systems. If this explanation is possibly true, it shows that Aquinas is wrong in thinking that "whatever lacks knowledge cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence."
b. The Argument from Simple Analogy
The next important version of the design argument came in the 17th and 18th Centuries. Pursuing a strategy that has been adopted by the contemporary intelligent design movement, John Ray, Richard Bentley, and William Derham drew on scientific discoveries of the 16th and 17th Century to argue for the existence of an intelligent Deity. William Derham, for example, saw evidence of intelligent design in the vision of birds, the drum of the ear, the eye-socket, and the digestive system. Richard Bentley saw evidence of intelligent design in Newton's discovery of the law of gravitation. It is noteworthy that each of these thinkers attempted to give scientifically-based arguments for the existence of God.
David Hume is the most famous critic of these arguments. In Part II of his famous Dialogues Concerning Natural Religion, Hume formulates the argument as follows:
Look round the world: contemplate the whole and every part of it: you will find it to be nothing but one great machine, subdivided into an infinite number of lesser machines, which again admit of subdivisions to a degree beyond what human senses and faculties can trace and explain. All these various machines, and even their most minute parts, are adjusted to each other with an accuracy which ravishes into admiration all men who have ever contemplated them. The curious adapting of means to ends, throughout all nature, resembles exactly, though it much exceeds, the productions of human contrivance; of human designs, thought, wisdom, and intelligence. Since, therefore, the effects resemble each other, we are led to infer, by all the rules of analogy, that the causes also resemble; and that the Author of Nature is somewhat similar to the mind of man, though possessed of much larger faculties, proportioned to the grandeur of the work which he has executed. By this argument a posteriori, and by this argument alone, do we prove at once the existence of a Deity, and his similarity to human mind and intelligence.
Since the world, on this analysis, is closely analogous to the most intricate artifacts produced by human beings, we can infer "by all the rules of analogy" the existence of an intelligent designer who created the world. Just as the watch has a watchmaker, then, the universe has a universe-maker.
As expressed in this passage, then, the argument is a straightforward argument from analogy with the following structure:
- The material universe resembles the intelligent productions of human beings in that it exhibits design.
- The design in any human artifact is the effect of having been made by an intelligent being.
- Like effects have like causes.
- Therefore, the design in the material universe is the effect of having been made by an intelligent creator.
Hume criticizes the argument on two main grounds. First, Hume rejects the analogy between the material universe and any particular human artifact. As Hume states the relevant rule of analogy, "wherever you depart in the least, from the similarity of the cases, you diminish proportionably the evidence; and may at last bring it to a very weak analogy, which is confessedly liable to error and uncertainty" (Hume, Dialogues, Part II). Hume then goes on to argue that the cases are simply too dissimilar to support an inference that they are like effects having like causes:
If we see a house,… we conclude, with the greatest certainty, that it had an architect or builder because this is precisely that species of effect which we have experienced to proceed from that species of cause. But surely you will not affirm that the universe bears such a resemblance to a house that we can with the same certainty infer a similar cause, or that the analogy is here entire and perfect (Hume, Dialogues, Part II).
Since the analogy fails, Hume argues that we would need to have experience with the creation of material worlds in order to justify any a posteriori claims about the causes of any particular material world; since we obviously lack such experience, we lack adequate justification for the claim that the material universe has an intelligent cause.
Second, Hume argues that, even if the resemblance between the material universe and human artifacts justified thinking they have similar causes, it would not justify thinking that an all-perfect God exists and created the world. For example, there is nothing in the argument that would warrant the inference that the creator of the universe is perfectly intelligent or perfectly good. Indeed, Hume argues that there is nothing there that would justify thinking even that there is just one deity: "what shadow of an argument... can you produce from your hypothesis to prove the unity of the Deity? A great number of men join in building a house or ship, in rearing a city, in framing a commonwealth; why may not several deities combine in contriving and framing a world" (Hume Dialogues, Part V)?
c. Paley's Watchmaker Argument
Though often confused with the argument from simple analogy, the watchmaker argument from William Paley is a more sophisticated design argument that attempts to avoid Hume's objection to the analogy between worlds and artifacts. Instead of simply asserting a similarity between the material world and some human artifact, Paley's argument proceeds by identifying what he takes to be a reliable indicator of intelligent design:
[S]uppose I found a watch upon the ground, and it should be inquired how the watch happened to be in that place, I should hardly think … that, for anything I knew, the watch might have always been there. Yet why should not this answer serve for the watch as well as for [a] stone [that happened to be lying on the ground]?… For this reason, and for no other; namely, that, if the different parts had been differently shaped from what they are, if a different size from what they are, or placed after any other manner, or in any order than that in which they are placed, either no motion at all would have been carried on in the machine, or none which would have answered the use that is now served by it (Paley 1867, 1).
There are thus two features of a watch that reliably indicate that it is the result of an intelligent design. First, it performs some function that an intelligent agent would regard as valuable; the fact that the watch performs the function of keeping time is something that has value to an intelligent agent. Second, the watch could not perform this function if its parts and mechanisms were differently sized or arranged; the fact that the ability of a watch to keep time depends on the precise shape, size, and arrangement of its parts suggests that the watch has these characteristics because some intelligent agency designed it to these specifications. Taken together, these two characteristics endow the watch with a functional complexity that reliably distinguishes objects that have intelligent designers from objects that do not.
Paley then goes on to argue that the material universe exhibits the same kind of functional complexity as a watch:
Every indicator of contrivance, every manifestation of design, which existed in the watch, exists in the works of nature; with the difference, on the side of nature, of being greater and more, and that in a degree which exceeds all computation. I mean that the contrivances of nature surpass the contrivances of art, in the complexity, subtilty, and curiosity of the mechanism; and still more, if possible, do they go beyond them in number and variety; yet in a multitude of cases, are not less evidently mechanical, not less evidently contrivances, not less evidently accommodated to their end, or suited to their office, than are the most perfect productions of human ingenuity (Paley 1867, 13).
Since the works of nature possess functional complexity, a reliable indicator of intelligent design, we can justifiably conclude that these works were created by an intelligent agent who designed them to instantiate this property.
Paley's watchmaker argument is clearly not vulnerable to Hume's criticism that the works of nature and human artifacts are too dissimilar to infer that they are like effects having like causes. Paley's argument, unlike arguments from analogy, does not depend on a premise asserting a general resemblance between the objects of comparison. What matters for Paley's argument is that works of nature and human artifacts have a particular property that reliably indicates design. Regardless of how dissimilar any particular natural object might otherwise be from a watch, both objects exhibit the sort of functional complexity that warrants an inference that it was made by an intelligent designer.
Paley's version of the argument, however, is generally thought to have been refuted by Charles Darwin's competing explanation for complex organisms. In The Origin of the Species, Darwin argued that more complex biological organisms evolved gradually over millions of years from simpler organisms through a process of natural selection. As Julian Huxley describes the logic of this process:
The evolutionary process results immediately and automatically from the basic property of living matter—that of self-copying, but with occasional errors. Self-copying leads to multiplication and competition; the errors in self-copying are what we call mutations, and mutations will inevitably confer different degrees of biological advantage or disadvantage on their possessors. The consequence will be differential reproduction down the generations—in other words, natural selection (Huxley 1953, 4).
Over time, the replication of genetic material in an organism results in mutations that give rise to new traits in the organism's offspring. Sometimes these new traits are so unfavorable to a being's survival prospects that beings with the traits die off; but sometimes these new traits enable the possessors to survive conditions that kill off beings without them. If the trait is sufficiently favorable, only members of the species with the trait will survive. By this natural process, functionally complex organisms gradually evolve over millions of years from primordially simple organisms.
Contemporary biologist, Richard Dawkins (1986), uses a programming problem to show that the logic of the process renders the Darwinian explanation significantly more probable than the design explanation. Dawkins considers two ways in which one might program a computer to generate the following sequence of characters: METHINKS IT IS LIKE A WEASEL. The first program randomly producing a new 28-character sequence each time it is run; since the program starts over each time, it incorporates a "single-step selection process." The probability of randomly generating the target sequence on any given try is 2728 (that is, 27 characters selected for each of the 28 positions in the sequence), which amounts to about 1 in (10,000 x 1,000,0006). While a computer running eternally would eventually produce the sequence, Dawkins estimates that it would take 1,000,0005 years—which is 1,000,0003 years longer than the universe has existed. As is readily evident, a program that selects numbers by means of such a "single-step selection mechanism" has a very low probability of reaching the target.
The second program incorporates a "cumulative-step selection mechanism." It begins by randomly generating a 28-character sequence of letters and spaces and then "breeds" from this sequence in the following way. For a specified period of time, it generates copies of itself; most of the copies perfectly replicate the sequence, but some copies have errors (or mutations). At the end of this period, it compares all of the sequences with the target sequence METHINKS IT IS LIKE A WEASEL and keeps the sequence that most closely resembles it. For example, a sequence that has an E in the second place more closely resembles a sequence that is exactly like the first except that it has a Q in the second place. It then begins breeding from this new sequence in exactly the same way. Unlike the first program which starts afresh with each try, the second program builds on previous steps, getting successively closer to the program as it breeds from the sequence closest to the target. This feature of the program increases the probability of reaching the sequence to such an extent that a computer running this program hit the target sequence after 43 generations, which took about half-an-hour.
The problem with Paley's watchmaker argument, as Dawkins explains it, is that it falsely assumes that all of the other possible competing explanations are sufficiently improbable to warrant an inference of design. While this might be true of explanations that rely entirely on random single-step selection mechanisms, this is not true of Darwinian explanations. As is readily evident from Huxley's description of the process, Darwinian evolution is a cumulative-step selection method that closely resembles in general structure the second computer program. The result is that the probability of evolving functionally complex organisms capable of surviving a wide variety of conditions is increased to such an extent that it exceeds the probability of the design explanation.
d. Guided Evolution
While many theists are creationists who accept the occurrence of "microevolution" (that is, evolution that occurs within a species, such as the evolution of penicillin-resistant bacteria) but deny the occurrence of "macroevolution" (that is, one species evolving from a distinct species), some theists accept the theory of evolution as consistent with theism and with their own denominational religious commitments. Such thinkers, however, frequently maintain that the existence of God is needed to explain the purposive quality of the evolutionary process. Just as the purposive quality of the cumulative-step computer program above is best explained by intelligent design, so too the purposive quality of natural selection is best explained by intelligent design.
The first theist widely known to have made such an argument is Frederick Robert Tennant. As he puts the matter, in Volume 2 of Philosophical Theology, "the multitude of interwoven adaptations by which the world is constituted a theatre of life, intelligence, and morality, cannot reasonably be regarded as an outcome of mechanism, or of blind formative power, or aught but purposive intelligence" (Tennant 1928-30, 121). In effect, this influential move infers design, not from the existence of functionally complex organisms, but from the purposive quality of the evolutionary process itself. Evolution is, on this line of response, guided by an intelligent Deity.
2. Contemporary Versions of the Design Argument
Contemporary versions of the design argument typically attempt to articulate a more sophisticated strategy for detecting evidence of design in the world. These versions typically contain three main elements—though they are not always explicitly articulated. First, they identify some property P that is thought to be a probabilistically reliable index of design in the following sense: a design explanation for P is significantly more probable than any explanation that relies on chance or random processes. Second they argue that some feature or features of the world exhibits P. Third, they conclude that the design explanation is significantly more likely to be true.
As we will see, however, all of the contemporary versions of the design inference seem to be vulnerable to roughly the same objection. While each of the design inferences in these arguments has legitimate empirical uses, those uses occur only in contexts where we have strong antecedent reason for believing there exist intelligent agents with the ability to bring about the relevant event, entity, or property. But since it is the very existence of such a being that is at issue in the debates about the existence of God, design arguments appear unable to stand by themselves as arguments for God's existence.
a. The Argument from Irreducible Biochemical Complexity
Design theorists distinguish two types of complexity that can be instantiated by any given structure. As William Dembski describes the distinction: a system or structure is cumulatively complex "if the components of the system can be arranged sequentially so that the successive removal of components never leads to the complete loss of function"; a system or structure is irreducibly complex "if it consists of several interrelated parts so that removing even one part completely destroys the system's function" (Dembski 1999, 147). A city is cumulatively complex since one can successively remove people, services, and buildings without rendering it unable to perform its function. A mousetrap, in contrast, is irreducibly complex because the removal of even one part results in complete loss of function.
Design proponents, like Michael J. Behe, have identified a number of biochemical systems that they take to be irreducibly complex. Like the functions of a watch or a mousetrap, a cilium cannot perform its function unless its microtubules, nexin linkers, and motor proteins are all arranged and structured in precisely the manner in which they are structured; remove any component from the system and it cannot perform its function. Similarly, the blood-clotting function cannot perform its function if either of its key ingredients, vitamin K and antihemophilic factor, are missing. Both systems are, on this view, irreducibly complex—rather than cumulatively complex.
According to Behe, the probability of evolving irreducibly complex systems along Darwinian lines is sufficiently small that it can be ruled out as an explanation of irreducible biochemical complexity:
An irreducibly complex system cannot be produced … by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional…. Since natural selection can only choose systems that are already working, if a biological system cannot be produced gradually it would have to arise as an integrated unit, in one fell swoop, for natural selection to have anything to act on (Behe 1996, 39; emphasis added).
Since, for example, a cilium-precursor (that is, one that lacks at least one of a cilium's parts) cannot perform the function that endows a cilium with adaptive value, organisms that have the cilium-precursor are no "fitter for survival" than they would have been without it. Since chance-driven evolutionary processes would not select organisms with the precursor, intelligent design is a better explanation for the existence of organisms with fully functional cilia.
Though Behe states his conclusion in categorical terms (that is, irreducibly complex systems "cannot be produced gradually"), he is more charitably construed as claiming only that the probability of gradually producing irreducibly complex systems is very small. The stronger construction of the conclusion (and argument) incorrectly presupposes that Darwinian theory implies that every precursor to a fully functional system must itself perform some function that makes the organism more fit to survive. Organisms that have, say, a precursor to a fully functional cilium are no fitter than they would have been without it, but there is nothing in Darwinian theory that implies they are necessarily any less fit. Thus, there is no reason to think that it is logically or nomologically impossible, according to Darwinian theory, for a set of organisms with a precursor to a fully functional cilium to evolve into a set of organisms that has fully functional cilia. Accordingly, the argument from irreducible biochemical complexity is more plausibly construed as showing that the design explanation for such complexity is more probable than the evolutionary explanation.
Nevertheless, this more modest interpretation is problematic. First, there is little reason to think that the probability of evolving irreducibly complex systems is, as a general matter, small enough to warrant assuming that the probability of the design explanation must be higher. If having a precursor to an irreducibly complex system does not render the organism less fit for survival, the probability a subspecies of organisms with the precursor survives and propagates is the same, other things being equal, as the probability that a subspecies of organisms without the precursor survives and propagates. In such cases, then, the prospect that the subspecies with the precursor will continue to thrive, leave offspring, and evolve is not unusually small.
Second, the claim that intelligent agents of a certain kind would (or should) see functional value in a complex system, by itself, says very little about the probability of any particular causal explanation. While this claim surely implies that intelligent agents with the right causal abilities have a reason for bringing about such systems, it does not tell us anything determinate about whether it is likely that intelligent agents with the right causal powers did bring such systems about—because it does not tell us anything determinate about whether it is probable that such agents exist. As a logical matter, the mere fact that some existing thing has a feature, irreducibly complex or otherwise, that would be valuable to an intelligent being with certain properties, by itself, does not say anything about the probability that such a being exists.
Accordingly, even if we knew that the prospect that the precursor-subspecies would survive was "vanishingly small," as Behe believes, we would not be justified in inferring a design explanation on probabilistic grounds. To infer that the design explanation is more probable than an explanation of vanishingly small probability, we need some reason to think that the probability of the design explanation is not vanishingly small. The problem, however, is that the claim that a complex system has some property that would be valued by an intelligent agent with the right abilities, by itself, simply does not justify inferring that the probability that such an agent exists and brought about the existence of that system is not vanishingly small. In the absence of some further information about the probability that such an agent exists, we cannot legitimately infer design as the explanation of irreducible biochemical complexity.
b. The Argument from Biological Information
While the argument from irreducible biochemical complexity focuses on the probability of evolving irreducibly complex living systems or organisms from simpler living systems or organisms, the argument from biological information focuses on the problem of generating living organisms in the first place. Darwinian theories are intended only to explain how it is that more complex living organisms developed from primordially simple living organisms, and hence do not even purport to explain the origin of the latter. The argument from biological information is concerned with an explanation of how it is that the world went from a state in which it contained no living organisms to a state in which it contained living organisms; that is to say, it is concerned with the explanation of the very first forms of life.
There are two distinct problems involved in explaining the origin of life from a naturalistic standpoint. The first is to explain how it is that a set of non-organic substances could combine to produce the amino acids that are the building blocks of every living substance. The second is to explain the origin of the information expressed by the sequences of nucleotides that form DNA molecules. The precise ordering of the four nucleotides, adenine, thymine, guanine, and cytosine (A, T, G, and C, for short), determine the specific operations that occur within a living cell and is hence fairly characterized as representing (or embodying) information. As Stephen C. Meyer puts the point: "just as the letters in the alphabet of a written language may convey a particular message depending on their sequence, so too do the sequences of nucleotides or bases in the DNA molecule convey precise biochemical instructions that direct protein synthesis within the cell" (Meyer 1998, 526).
The argument from biological information is concerned with only the second of these problems. In particular, it attempts to evaluate four potential explanations for the origin of biological information: (1) chance; (2) a pre-biotic form of natural selection; (3) chemical necessity; and (4) intelligent design. The argument concludes that intelligent design is the most probable explanation for the information present in large biomacromolecules like DNA, RNA, and proteins.
The argument proceeds as follows. Pre-biotic natural selection and chemical necessity cannot, as a logical matter, explain the origin of biological information. Theories of pre-biotic natural selection are problematic because they illicitly assume the very feature they are trying to explain. These explanations proceed by asserting that the most complex nonliving molecules will reproduce more efficiently than less complex nonliving molecules. But, in doing so, they assume that nonliving chemicals instantiate precisely the kind of replication mechanism that biological information is needed to explain in the case of living organisms. In the absence of some sort of explanation as to how non-organic reproduction could occur, theories of pre-biotic natural selection fail.
Theories of chemical necessity are problematic because chemical necessity can explain, at most, the development of highly repetitive ordered sequences incapable of representing information. Because processes involving chemical necessity are highly regular and predictable in character, they are capable of producing only highly repetitive sequences of "letters." For example, while chemical necessity could presumably explain a sequence like "ababababababab," it cannot explain specified but highly irregular sequences like "the house is on fire." The problem is that highly repetitive sequences like the former are not sufficiently complex and varied to express information. Thus, while chemical necessity can explain periodic order among nucleotide letters, it lacks the resources logically needed to explain the aperiodic, highly specified, complexity of a sequence capable of expressing information.
Ultimately, this leaves only chance and design as logically viable explanations of biological information. Although it is logically possible to obtain functioning sequences of amino acids through purely random processes, some researchers have estimated the probability of doing so under the most favorable of assumptions at approximately 1 in 1065. Factoring in more realistic assumptions about pre-biotic conditions, Meyer argues the probability of generating short functional protein is 1 in 10125—a number that is vanishingly small. Meyer concludes: "given the complexity of proteins, it is extremely unlikely that a random search through all the possible amino acid sequences could generate even a single relatively short functional protein in the time available since the beginning of the universe (let alone the time available on the early earth)" (Meyer 2002, 75).
Next, Meyer argues that the probability of the design explanation for the origin of biological information is considerably higher:
[O]ne can detect the past action of an intelligent cause from the presence of an information-rich effect, even if the cause itself cannot be directly observed. For instances, visitors to the gardens of Victoria harbor in Canada correctly infer the activity of intelligent agents when they see a pattern of red and yellow flowers spelling "Welcome to Victoria", even if they did not see the flowers planted and arranged. Similarly, the specifically arranged nucleotide sequences—the complex but functionally specified sequences—in DNA imply the past action of an intelligent mind, even if such mental agency cannot be directly observed (Meyer 2002, 93).
Further, scientists in many fields typically infer the causal activity of intelligent agents from the occurrence of information content. As Meyer rightly observes by way of example, "[a]rcheologists assume a mind produced the inscriptions on the Rosetta Stone" (Meyer 2002, 94).
Meyer's reasoning appears vulnerable to the same objection to which the argument from biochemical complexity is vulnerable. In all of the contexts in which we legitimately make the design inference in response to an observation of information, we already know that there exist intelligent agents with the right sorts of motivations and abilities to produce information content; after all, we know that human beings exist and are frequently engaged in the production and transmission of information. It is precisely because we have this background knowledge that we can justifiably be confident that intelligent design is a far more probable explanation than chance for any occurrence of information that a human being is capable of producing. In the absence of antecedent reason for thinking there exist intelligent agents capable of creating information content, the occurrence of a pattern of flowers in the shape of "Welcome to Victoria" would not obviously warrant an inference of intelligent design.
The problem, however, is that it is the very existence of an intelligent Deity that is at issue. In the absence of some antecedent reason for thinking there exists an intelligent Deity capable of creating biological information, the occurrence of sequences of nucleotides that can be described as "representing information" does not obviously warrant an inference of intelligent design—no matter how improbable the chance explanation might be. To justify preferring one explanation as more probable than another, we must have information about the probability of each explanation. The mere fact that certain sequences take a certain shape that we can see meaning or value in, by itself, tells us nothing obvious about the probability that it is the result of intelligent design.
It is true, of course, that "experience affirms that information content not only routinely arises but always arises from the activity of intelligent minds" (Meyer 2002, 92), but our experience is limited to the activity of human beings—beings that are frequently engaged in activities that are intended to produce information content. While that experience will inductively justify inferring that some human agency is the cause of any information that could be explained by human beings, it will not inductively justify inferring the existence of an intelligent agency with causal powers that depart as radically from our experience as the powers that are traditionally attributed to God. The argument from biological information, like the argument from biochemical complexity, seems incapable of standing alone as an argument for God's existence.
c. The Fine-Tuning Arguments
Scientists have determined that life in the universe would not be possible if more than about two dozen properties of the universe were even slightly different from what they are; as the matter is commonly put, the universe appears "fine-tuned" for life. For example, life would not be possible if the force of the big bang explosion had differed by one part in 1060; the universe would have either collapsed on itself or expanded too rapidly for stars to form. Similarly, life would not be possible if the force binding protons to neutrons differed by even five percent.
It is immediately tempting to think that the probability of a fine-tuned universe is so small that intelligent design simply must be the more probable explanation. The supposition that it is a matter of chance that so many things could be exactly what they need to be for life to exist in the universe just seems implausibly improbable. Since, on this intuition, the only two explanations for the highly improbable appearance of fine-tuning are chance and an intelligent agent who deliberately designed the universe to be hospitable to life, the latter simply has to be the better explanation.
This natural line of argument is vulnerable to a cogent objection. The mere fact that it is enormously improbable that an event occurred by chance, by itself, gives us no reason to think that it occurred by design. Suppose we flip a fair coin 1000 times and record the results in succession. The probability of getting the particular outcome is vanishingly small: 1 in 21000 to be precise. But it is clear that the mere fact that such a sequence is so improbable, by itself, does not give us any reason to think that it was the result of intelligent design. As intuitively tempting as it may be to conclude from just the apparent improbability of a fine-tuned universe that it is the result of divine agency, the inference is unsound.
i. The Argument from Suspicious Improbabilitys
George N. Schlesinger, however, attempts to formalize the fine-tuning intuition in a way that avoids this objection. To understand Schlesinger's argument, consider your reaction to two different events. If John wins a 1-in-1,000,000,000 lottery game, you would not immediately be tempted to think that John (or someone acting on his behalf) cheated. If, however, John won three consecutive 1-in-1,000 lotteries, you would immediately be tempted to think that John (or someone acting on his behalf) cheated. Schlesinger believes that the intuitive reaction to these two scenarios is epistemically justified. The structure of the latter event is such that it is justifies a belief that intelligent design is the cause: the fact that John got lucky in three consecutive lotteries is a reliable indicator that his winning was the intended result of someone's intelligent agency. Despite the fact that the probability of winning three consecutive 1-in-1,000 games is exactly the same as the probability of winning one 1-in-1,000,000,000 game, the former event is of a kind that is surprising in a way that warrants an inference of intelligent design.
Schlesinger argues that the fact that the universe is fine-tuned for life is improbable in exactly the same way that John's winning three consecutive lotteries is improbable. After all, it is not just that we got lucky with respect to one property-lottery game; we got lucky with respect to two dozen property-lottery games—lotteries that we had to win in order for there to be life in the universe. Given that we are justified in inferring intelligent design in the case of John's winning three consecutive lotteries, we are even more justified in inferring intelligent design in the case of our winning two dozen much more improbable property lotteries. Thus, Schlesinger concludes, the most probable explanation for the remarkable fact that the universe has exactly the right properties to sustain life is that an intelligent Deity intentionally created the universe such as to sustain life.
This argument is vulnerable to a number of criticisms. First, while it might be clear that carbon-based life would not be possible if the universe were slightly different with respect to these two-dozen fine-tuned properties, it is not clear that no form of life would be possible. Second, some physicists speculate that this physical universe is but one material universe in a "multiverse" in which all possible material universes are ultimately realized. If this highly speculative hypothesis is correct, then there is nothing particularly suspicious about the fact that there is a fine-tuned universe, since the existence of such a universe is inevitable (that is, has probability 1) if all every material universe is eventually realized in the multiverse. Since some universe, so to speak, had to win, the fact that ours won does not demand any special explanation.
Schlesinger's fine-tuning argument also appears vulnerable to the same criticism as the other versions of the design argument (see Himma 2002). While Schlesinger is undoubtedly correct in thinking that we are justified in suspecting design in the case where John wins three consecutive lotteries, it is because—and only because—we know two related empirical facts about such events. First, we already know that there exist intelligent agents who have the right motivations and causal abilities to deliberately bring about such events. Second, we know from past experience with such events that they are usually explained by the deliberate agency of one or more of these agents. Without at least one of these two pieces of information, we are not obviously justified in seeing design in such cases.
As before, the problem for the fine-tuning argument is that we lack both of the pieces that are needed to justify an inference of design. First, the very point of the argument is to establish the fact that there exists an intelligent agency that has the right causal abilities and motivations to bring the existence of a universe capable of sustaining life. Second, and more obviously, we do not have any past experience with the genesis of worlds and are hence not in a position to know whether the existence of fine-tuned universes are usually explained by the deliberate agency of some intelligent agency. Because we lack this essential background information, we are not justified in inferring that there exists an intelligent Deity who deliberately created a universe capable of sustaining life.
ii. The Confirmatory Argument
Robin Collins defends a more modest version of the fine-tuning argument that relies on a general principle of confirmation theory, rather than a principle that is contrived to distinguish events or entities that are explained by intelligent design from events or entities explained by other factors. Collins's version of the argument relies on what he calls the Prime Principle of Confirmation: If observation O is more probable under hypothesis H1 than under hypothesis H2, then O provides a reason for preferring H1 over H2. The idea is that the fact that an observation is more likely under the assumption that H1 is true than under the assumption H2 is true counts as evidence in favor of H1.
This version of the fine-tuning argument proceeds by comparing the relative likelihood of a fine-tuned universe under two hypotheses:
- The Design Hypothesis: there exists a God who created the universe such as to sustain life;
- The Atheistic Single-Universe Hypothesis: there exists one material universe, and it is a matter of chance that the universe has the fine-tuned properties needed to sustain life.
Assuming the Design Hypothesis is true, the probability that the universe has the fine-tuned properties approaches (if it does not equal) 1. Assuming the Atheistic Single-Universe Hypothesis is true, the probability that the universe has the fine-tuned properties is very small—though it is not clear exactly how small. Applying the Prime Principle of Confirmation, Collins concludes that the observation of fine-tuned properties provides reason for preferring the Design Hypothesis over the Atheistic Single-Universe Hypothesis.
At the outset, it is crucial to note that Collins does not intend the fine-tuned argument as a proof of God's existence. As he explains, the Prime Principle of Confirmation "is a general principle of reasoning which tells us when some observation counts as evidence in favor of one hypothesis over another" (Collins 1999, 51). Indeed, he explicitly acknowledges that "the argument does not say that the fine-tuning evidence proves that the universe was designed, or even that it is likely that the universe was designed" (Collins 1999, 53). It tells us only that the observation of fine-tuning provides one reason for accepting the Theistic Hypothesis over the Atheistic Single-Universe Hypothesis—and one that can be rebutted by other evidence.
The confirmatory version of the fine-tuning argument is not vulnerable to the objection that it relies on an inference strategy that presupposes that we have independent evidence for thinking the right kind of intelligent agency exists. As a general scientific principle, the Prime Principle of Confirmation can be applied in a wide variety of circumstances and is not limited to circumstances in which we have other reasons to believe the relevant conclusion is true. If the observation of a fine-tuned universe is more probable under the Theistic Hypothesis than under the Atheistic Single-Universe Hypothesis, then this fact is a reason for preferring the Design Hypothesis to Atheistic Single-Universe Hypothesis.
Nevertheless, the confirmatory version of the argument is vulnerable on other fronts. As a first step towards seeing one worry, consider two possible explanations for the observation that John Doe wins a 1-in-7,000,000 lottery (see Himma 2002). According to the Theistic Lottery Hypothesis, God wanted John Doe to win and deliberately brought it about that his numbers were drawn. According to the Chance Lottery Hypothesis, John Doe's numbers were drawn by chance. It is clear that John's winning the lottery is vastly more probable under the Theistic Lottery Hypothesis than under the Chance Lottery Hypothesis. By the Prime Principle of Confirmation, then, John's winning the lottery provides a reason to prefer the Theistic Lottery Hypothesis over the Chance Lottery Hypothesis.
As is readily evident, the above reasoning, by itself, provides very weak support for the Theistic Lottery Hypothesis. If all we know about the world is that John Doe won a lottery and the only possible explanations for this observation are the Theistic Lottery Hypothesis and the Chance Lottery Hypothesis, then this observation provides some reason to prefer the former. But it does not take much counterevidence to rebut the Theistic Lottery Hypothesis: a single observation of a lottery that relies on a random selection process will suffice. A single application of the Prime Principle of Confirmation, by itself, is simply not designed to provide the sort of reason that would warrant much confidence in preferring one hypothesis to another.
For this reason, the confirmatory version of the fine-tuning argument, by itself, provides a weak reason for preferring the Design Hypothesis over the Atheistic Single Universe Hypothesis. Although Collins is certainly correct in thinking the observation of fine-tuning provides a reason for accepting the Design Hypothesis and hence rational ground for belief that God exists, that reason is simply not strong enough to do much in the way of changing the minds of either agnostics or atheists.
3. The Scientifically Legitimate Uses of Design Inferences
It is worth noting that proponents are correct in thinking that design inferences have a variety of legitimate scientific uses. Such inferences are used to detect intelligent agency in a large variety of contexts, including criminal and insurance investigations. Consider, for example, the notorious case of Nicholas Caputo. Caputo, a member of the Democratic Party, was a public official responsible for conducting drawings to determine the relative ballot positions of Democrats and Republicans. During Caputo's tenure, the Democrats drew the top ballot position 40 of 41 times, making it far more likely that an undecided voter would vote for the Democratic candidate than for the Republican candidate. The Republican Party filed suit against Caputo, arguing he deliberately rigged the ballot to favor his own party. After noting that the probability of picking the Democrats 40 out of 41 times was less than 1 in 50 billion, the court legitimately made a design inference, concluding that "few persons of reason will accept the explanation of blind chance."
What proponents of design arguments for God's existence, however, have not noticed is that each one of these indubitably legitimate uses occurs in a context in which we are already justified in thinking that intelligent beings with the right motivations and abilities exist. In every context in which design inferences are routinely made by scientists, they already have conclusive independent reason for believing there exist intelligent agents with the right abilities and motivations to bring about the apparent instance of design.
Consider, for example, how much more information was available to the court in the Caputo case than is available to the proponent of the design argument for God's existence. Like the proponent of the design argument, the court knew that (1) the relevant event or feature is something that might be valued by an intelligent agent; and (2) the odds of it coming about by chance are astronomically small. Unlike the proponent of the design argument, however, the court had an additional piece of information available to it: the court already knew that there existed an intelligent agent with the right causal abilities and motives to bring about the event; after all, there was no dispute whatsoever about the existence of Caputo. It was that piece of information, together with (1), that enabled the court to justifiably conclude that the probability that an intelligent agent deliberately brought it about that the Democrats received the top ballot position 40 of 41 times was significantly higher than the probability that this happened by chance. Without this crucial piece of information, however, the court would not have been so obviously justified in making the design inference. Accordingly, while the court was right to infer a design explanation in the Caputo case, this is, in part, because the judges already knew that the right kind of intelligent beings exist—and one of them happened to have occupied a position that afforded him with the opportunity to rig the drawings in favor of the Democrats.
In response, one might be tempted to argue that there is one context in which scientists employ the design inference without already having sufficient reason to think the right sort of intelligent agency exists. As is well-known, researchers monitor radio transmissions for patterns that would support a design inference that such transmissions are sent by intelligent beings. For example, it would be reasonable to infer that some intelligent extraterrestrial beings were responsible for a transmission of discrete signals and pauses that effectively enumerated the prime numbers from 2 to 101. In this case, the intelligibility of the pattern, together with the improbability of its occurring randomly, seems to justify the inference that the transmission sequence is the result of intelligent design.
As it turns out, we are already justified in thinking that the right sort of intelligent beings exist even in this case. We already know, after all, that we exist and have the right sort of motivations and abilities to bring about such transmissions because we send them into space hoping that some other life form will detect our existence. While our existence in the universe—and this is crucial—does not, by itself, justify thinking that there are other intelligent life forms in the universe, it does justify thinking that the probability that there are such life forms is higher than the astronomically small probability (1 in 21136 to be precise) that a sequence of discrete radio signals and pauses that enumerates the prime numbers from 2 to 101 is the result of chance. Thus, we would be justified in inferring design as the explanation of such a sequence on the strength of three facts: (1) the probability of such a chance occurrence is 1 in 21136; (2) there exist intelligent beings in the universe capable of bringing about such an occurrence; and (3) the sequence of discrete signals and pauses has a special significance to intelligent beings. In particular, (2) and (3) tell us that the probability that design explains such an occurrence is significantly higher than 1 in 21136—though it is not clear exactly what the probability is.
Insofar as the legitimate application of design inferences presupposes that we have antecedent reason to believe the right kind of intelligent being exists, they can enable us to distinguish what such beings do from what merely happens. If we already know, for example, that there exist beings capable of rigging a lottery, then design inferences can enable us to distinguish lottery results that merely happen from lottery results that are deliberately brought about by such agents. Similarly, if we already have adequate reason to believe that God exists, then design inferences can enable us to distinguish features of the world that merely happen from features of the world that are deliberately brought about by the agency of God. Indeed, to the extent that we are antecedently justified in believing that God exists, it is obviously more reasonable to believe that God deliberately structured the universe to have the fine-tuned properties than it is to believe that somehow this occurred by chance.
If this is correct, then design inferences simply cannot do the job they are asked to do in design arguments for God's existence. Insofar as they presuppose that we already know the right kind of intelligent being exists, they cannot stand alone as a justification for believing that God exists. It is the very existence of the right kind of intelligent being that is at issue in the dispute over whether God exists. While design inferences have a variety of scientifically legitimate uses, they cannot stand alone as arguments for God's existence.
4. References and Further Reading
- Michael J. Behe, Darwin's Black Box: The Biochemical Challenge to Evolution (New York: Touchstone Books, 1996)
- Richard Bentley, A Confutation of Atheism from the Origin and Frame of the World (London: H. Mortlock, 1692-1693)
- Robin Collins, "A Scientific Argument for the Existence of God," in Michael J. Murray (ed.), Reason for the Hope Within (Grand Rapids, MI: William B. Eerdmans Publishing Co., 1999)
- Charles Darwin, The Origin of Species, Everyman's Library (London: J.M. Dent, 1947)
- Richard Dawkins, The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe without Design (New York: Norton Publishing, 1996; originally published in 1986)
- William Dembski, The Design Inference (Cambridge: Cambridge University Press, 1998)
- William Dembski, No Free Lunch: Why Specified Complexity Cannot Be Purchased without Intelligence (Rowman & Littlefield, 2002)
- William Derham, Physico-theology, or, A Demonstration of the Being and Attributes of God from his Works of Creation Being the Substance of XVI Sermons Preached in St. Mary le Bow-Church, London, at the Hon'ble Mr. Boyle's Lectures in the Years 1711 and 1712 (London: W. Innys, 1713)
- William Derham, Astro-theology, or, A Demonstration of the Being and Attributes of God: From a Survey of the Heavens (London: W. Innys, 1715)
- Kenneth Einar Himma, "Prior Probabilities and Confirmation Theory: A Problem with the Fine-Tuning Argument," International Journal for Philosophy of Religion, vol. 51, no. 4 (June 2002)
- Kenneth Einar Himma, "The Application-Conditions for Design Inferences: Why the Design Arguments Need the Help of Other Arguments for God's Existence,"International Journal for Philosophy of Religion., vol. 57, no. 1 (February 2005).
- David Hume, Dialogues Concerning Natural Religion, edited with an introduction by Norman Kemp Smith, (New York: Social Sciences Publishers, 1948)
- Julian Huxley, Evolution as Process (New York: Harper and Row, 1953).
- Stephen C. Meyer, "DNA by Design: An Inference to the Best Explanation," Rhetoric and Public Affairs, vol. 1, no. 4 (Winter 1998)
- Stephen C. Meyer, "Evidence for Design in Physics and Biology: From the Origin of the Universe to the Origin of Life," in Behe, Dembski, and Meyer (eds.), Science and Evidence for Design in the Universe (San Francisco: Ignatius Press, 2002)
- William Paley, Natural Theology: Or Evidences of the Existence and Attributes of the Deity Collected from the Appearances of Nature (Boston: Gould and Lincoln, 1867)
- Del Ratzsch, Nature, Design, and Science: The Status of Design in Natural Science (Albany, NY: SUNY Press, 2001)
- John Ray, The Wisdom of God Manifested in the Works of the Creation Being the Substance of Some Common Places Delivered in the Chappel of Trinity-College, in Cambridge (London: Printed for Samuel Smith, 1691)
- Hugh Ross, Beyond the Cosmos: What Recent Discoveries in Astronomy and Physics Reveal about the Nature of God (Colorado Springs: Nav Press, 1996)
- George N. Schlesinger, New Perspectives on Old-time Religion (Oxford: Clarendon Press, 1988)
- Frederick Robert Tennant, Philosophical Theology, Volume 2 (1928-30)
Kenneth Einar Himma
Seattle Pacific University
U. S. A.