International Journal for Philosophy of Religion 55: 65–68, 2004.© 2004 Kluwer Academic Publishers. Printed in the Netherlands.

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Book review

James Beilby (ed.), Naturalism Defeated? Essays on Plantinga’s Evolu-tionary Argument Against Naturalism. Ithaca, NY: Cornell University Press,2002, x and 283 pages, Hb $45.00, Pa $19.95

Alvin Plantinga claims that the objective probability of one’s cognitivefaculties being reliable (as opposed to merely adaptive), given that theyevolved without supernatural assistance by way of mechanisms like naturalselection, is either low or inscrutable. Letting “R” stand for the propositionthat our cognitive faculties are reliable, and letting “N” and “E” stand for(ontological) naturalism and (current) evolutionary theory, this claim can beexpressed symbolically as follows:

(1) Pr(R/N&E) is low or inscrutable.This is the first premise of Plantinga’s evolutionary argument against natur-alism. If we define an “informed naturalist” as an ontological naturalist whoboth knows whether or not (1) is true and realizes that evolution is almostcertainly true given ontological naturalism, then we can formulate the secondpremise of the argument as follows:

(2) If Pr(R/N&E) is low or inscrutable, then every informed naturalist hasa rationality defeater for R.

To flesh this out a bit, notice that, if (1) is true, then the informed naturalistwill believe that

D: (N&E) is true and Pr(R/N&E) is low or inscrutable.But, according to Plantinga, D is a rationality defeater for R: anyone whoaccepts D cannot rationally believe that their cognitive faculties are reliable.

Premises (1) and (2) together entail(3) Every informed naturalist has a rationality defeater for R (namely, the

belief that D).One should not, however, trust beliefs that one believes to be produced byunreliable cognitive faculties, which is why

(4) Anyone who has a rationality defeater for R has a rationality defeaterfor all of her other beliefs as well.

From (3) and (4), it follows that(5) Every informed naturalist has a rationality defeater for all of her

beliefs, including her belief in naturalism.

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Of course, some defeaters are themselves ultimately defeated. But not D, saysPlantinga. For any belief that one proposes to use as a defeater for D mustitself be a victim of defeat by D. Thus, we have

(6) This defeater is ultimately undefeated.

And from (5) and (6), Plantinga deduces

(7) Every informed naturalist has an ultimately undefeated rationalitydefeater for naturalism.

This is a fascinating argument. Whether or not it succeeds is the topic ofa splendid collection of essays edited by James Beilby. The book containsone reprinted and ten new essays criticizing Plantinga’s argument. It alsocontains a helpful preface by Beilby, a brief introductory essay by Plantingain which he explains the argument, and, best of all, a lengthy concludingessay, also by Plantinga, in which he refines his argument and then replies toeach of the other contributors individually. The book lacks a bibliography ofpreviously published work on Plantinga’s argument, but Plantinga cites therelevant secondary literature in the first footnote of his concluding essay.

Beilby points out in the preface that Plantinga’s argument raises issues ofinterest in a variety of philosophical subdisciplines. This is one of the reasonsthat the argument makes a wonderful topic for an edited collection. In fact, myonly major criticism of the book is that it doesn’t fully take advantage of thisopportunity. It has a decidedly strong bias towards epistemological issues,more or less relegating issues in the philosophy of mind and the philosophyof biology to the first three essays in the book, which are grouped under theheading “Science and Evolution.” Another issue that receives little attentionis whether the theist is in a better epistemic position than the naturalist withrespect to R (or with respect to R conjoined with the additional fact that ourcognitive faculties, though generally reliable, are prone to systematic error).This issue, which is of particular interest to philosophers of religion, receivesserious attention only by Evan Fales, though it is also briefly discussed byWilliam Ramsey, Ernest Sosa, and James Van Cleve. Another way in whichthe book lacks breadth concerns the repeated challenges to Plantinga’s secondpremise. While, as I will explain below, it is not surprising that most ofPlantinga’s critics challenge this premise, a number of these challenges arequite similar, and consequently both the book as a whole and Plantinga’sreplies to individual authors are at times a bit repetitive.

To understand why premise (2) is the favorite target of Plantinga’s critics,it is important to realize that neither of the two most natural interpretationsof Plantinga’s conditional probability in premise (1) is the correct interpre-tation. Pr(R/N&E) is not the probability of R, all things considered, on theassumption that N and E are true. (William Alston calls this the globalinterpretation.) Nor is it the degree to which R is made probable soley by

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(N&E). (Alston calls this the parochial interpretation.) The correct interpre-tation, as Alston explains in his essay, lies somewhere in between. Roughly,general background knowledge is presupposed, but not specific evidencefor R.

It is this exclusion of specific evidence for R that explains why so manyof the contributors to Beilby’s book have doubts about premise (2). Whilebelieving that a proposition is improbable all things considered is certainly agood reason not to believe that proposition, the significance of believing that aproposition is improbable relative to something other than the total evidenceis much less clear. To use one of Sosa’s examples, the fact that “this stoneis smooth” has low or inscrutable probability given its derivation from bruteforces hardly defeats the belief that the stone is smooth. Trenton Merricks andVan Cleve both believe that this is the Achilles’ heel of Plantinga’s argument.As Van Cleve says, “[the naturalist] will not have a defeater for R in themere fact that R has inscrutable probability given N&E. R will have highprobability with respect to his total noetic structure even if it has inscrutableprobability with respect to selected parts of it” (120). Richard Otte is alsoconcerned with the selective nature of Pr(R/N&E), arguing that, in order tomake premise (2) true, Plantinga must conditionalize on more than just N&E;he must conditionalize on N&E conjoined with a statement reporting one’sexperience.

Michael Bergmann makes essentially the same point as Merricks and VanCleve, but he makes it in a Reidian fashion (which of course resonates withPlantinga). He defends the position that we have non-propositional evidencefor R that prevents D from defeating R, at least when R is specified tooneself and not to others. A different strategy is adopted by W.J. Talbott, whoargues that, since we have evidence that our beliefs run up against objectiveconstraints, it follows that we have (propositional) evidence for R. Talbottadmits that this is a case of one’s own cognitive faculties judging themselvesto be reliable. But, making use of some ingenious analogies, he argues thatthere is no objectionable circularity here. Plantinga himself concedes that anaturalist would continue to believe R even after forming the belief that D,and that her cognitive faculties would be functioning properly in doing so. Hemaintains, however, that this is only because those faculties are concerned,not just with truth, but with avoiding cognitive disaster. He concludes that Dis still a “Humean” rationality defeater for R, meaning that in some situations(e.g. when reflecting on D and R in one’s study), proper functioning willrequire withholding belief in R.

Plantinga believes that analogies suffice to establish that other evidencefor R won’t protect it from defeat by D. One such analogy asks us to supposethat we come to believe we are the creation of a powerful demon who system-

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atically deceives the vast majority of his creatures. In such circumstances,rationality would require us to withhold belief in R, at least when practicalconsiderations permit us to do so, no matter how much initial warrant forR we had. Of course, this analogy supports premise (2) only if coming tobelieve (N&E) puts one in the same epistemic situation as coming to believein such a demon. It is not clear, however, that it does. For notice that theobjective probability of R given the existence of such a demon is low, notinscrutable. Jerry Fodor does not explicitly address this analogy, but he deniesthat Pr(R/N&E) is low. He accepts that Plantinga can show that our havingevolved (naturalistically) does not make it likely that our cognitive facultiesare reliable, but he denies that Plantinga can show that our having evolved(naturalistically) makes it likely that our cognitive faculties are unreliable. Heconcludes that Plantinga falls short of identifying a defeater for R. Alston andTimothy O’Connor echo Fodor’s point when they reject the claim, entailed bypremise (2), that, if Pr(R/N&E) is inscrutable, then every informed naturalisthas a defeater for R. They both wonder why the inscrutability of Pr(R/N&E)should bother naturalists, since naturalists have other evidence for R.

I have been emphasizing the similarities between the critical essays inBeilby’s book, but there are important differences as well, differences thatadd to the depth of the book. Moreover, the similarities give the book a greatdeal more cohesiveness than one would have expected to find in a collec-tion of essays by distinct authors, especially given the variety of interestingissues raised by Plantinga’s argument. Thus, my overall evaluation of thebook is very positive. Its depth and cohesiveness, as well the high quality ofthe individual essays it contains, “defeat” my initial criticism about limitedbreadth.

Paul DraperFlorida International University