Evolutionary argument against naturalism

The Evolutionary argument against naturalism (sometimes abbreviated EAAN) is a philosophical argument that metaphysical naturalism when combined with contemporary evolutionary accounts of the origin of human life is in a certain interesting way self-defeating. Although C. S. Lewis made somewhat similar observations, the argument as it is commonly presented was first put forward and has mostly been developed by Alvin Plantinga, a contemporary philosopher of epistemology at the University of Notre Dame.

C. S. Lewis

The general claim that naturalism undercuts its own justification was argued by C. S. Lewis in the third chapter of his book Miracles, as well as in numerous other writings. For instance, in "On Living in an Atomic Age" he claimed that “It is only through trusting our own minds that we have come to know Nature herself. If Nature, when fully known, seems to teach us (that is, if the sciences teach us) that our own minds are chance arrangements of atoms, then the sciences themselves would be chance arrangements of atoms and we should have no reason for believing them.”

Plantinga's Argument

Alvin Plantinga's argument attempts to show that combining naturalism and evolution is self-defeating because under these assumptions the probability that humans have reliable cognitive faculties is low or inscrutable. The argument has been published by the Oxford University Press in Warrant and Proper Function, and a presentation of the argument can be found on the web[1]. A more recent and extensive discussion is found in Naturalism Defeated? Cornell (2002), in which Plantinga sets out the argument, 11 philosophers comment and Plantinga responds.

Plantinga makes it clear that he is not attacking the theory of evolution, and introduces his argument with a quotation by Charles Darwin:

Charles Darwin in 1880.

With me, the horrid doubt always arises whether the convictions of man's mind, which has been developed from the mind of the lower animals, are of any value or at all trustworthy. Would anyone trust in the convictions of a monkey's mind...?

— Charles Darwin.

He defines:

• N as naturalism
• E as the belief that we human beings have evolved in conformity with current evolutionary doctrine
• R as the proposition that our faculties are "reliable", where, roughly, a cognitive faculty is "reliable" if the great bulk of its deliverances are true. He specifically cites a thermometer stuck at 72 degrees placed in an environment which happened to be at 72 degrees as an example of something that is not "reliable" in this sense

and suggests that P(R/N&E) is low.

Plantinga's argument begins with the observation that our beliefs can only have evolutionary consequences if they affect behaviour. To put this another way, natural selection does not directly select for true beliefs, but rather for advantageous behaviours. Plantinga distinguishes the various theories of mind-body interaction into four jointly exhaustive categories:

1. epiphenomenalism, where behaviour is not caused by beliefs. "if this way of thinking is right, beliefs would be invisible to evolution" so the P(R/N&E) would be low or inscrutable
2. Semantic epiphenomenalism, where beliefs has a causative link to behaviour but not by virtue of their semanticcontent. Under this theory, a belief would be some form of long-term neuronal event. However on this view P(R/N&E) would be low because the semantic content of beliefs would be invisible to natural selection, and it is semantic content that determines truth-value.
3. Beliefs are causally efficacious with respect to behaviour, but maladaptive, in which case he suggests P(R/N&E) would be low because R would be adversely selected for.
4. Beliefs are causally efficacious with respect to behaviour, and adaptive. Since behaviour is caused by both belief and desire and desire can lead to false belief, there are many ways in which beliefs could be false but adaptive and natural selection would have no reason for selecting true but non-adaptive beliefs over false but adaptive beliefs. Thus he suggests that P(R/N&E) in this case is also low. Plantinga points out that innumerable belief-desire pairs could account for a given behaviour; for example, that of a prehistoric man fleeing a tiger:

Perhaps Paul very much likes the idea of being eaten, but when he sees a tiger, always runs off looking for a better prospect, because he thinks it unlikely the tiger he sees will eat him. This will get his body parts in the right place so far as survival is concerned, without involving much by way of true belief... Or perhaps he thinks the tiger is a large, friendly, cuddly pussycat and wants to pet it; but he also believes that the best way to pet it is to run away from it... Clearly there are any number of belief-cum-desire systems that equally fit a given bit of behaviour.

Thus, Plantinga argues, the probability that our minds are reliable under a conjunction of philosophical naturalism and evolution is low or inscrutable. Thus, asserting that naturalistic evolution is true is also asserting that one has a low probability of being right in any of his assertions. This, Plantinga argues, epistemically defeats the belief that naturalistic evolution is true - ascribing truth to naturalism and evolution becomes self-referentially incoherent.

Plantinga contrasts the purely naturalistic-evolutionary view with the alternative theistic view that, while accepting the scientific description of evolutionary processes, also allows for the presence of a God who is capable of creating a universe, the physical properties of which produce reliable human cognitive faculties, even though the direct physical cause thereof is undirected (see, for example, the philosophical position known as theistic evolution).

Responses by critics

Naturalism Defeated? (2002)

In Naturalism Defeated? (2002) there are responses by 11 philosophers to Plantinga's arguments.

• William Ramsey argues that Plantinga “overlooks the most sensible way . . . to get clear on how truth can be a property of beliefs that bestows an advantage on cognitive systems”.
• Jerry Fodor argues that there is a plausible historical scenario according to which our minds were selected because their cognitive mechanisms produced, by and large, adaptive true beliefs.
• Evan Fales argues that Plantinga has not demonstrated that the reliability of our cognitive faculties is improbable, given Neo-Darwinism, and emphasizes, rightly, that “if Plantinga’s argument fails here, then he will not have shown that [N&E] is probabilistically incoherent”
• Michael Bergmann suggests that Thomas Reid offers the resources for a commonsense defense of naturalism against EAAN.
• Ernest Sosa draws on insufficiently appreciated features of Descartes’ epistemology to argue that while “[i]ssues of circularity do arise as to how we can rationally and knowledgeably adopt [an epistemically propitious] view about our own epistemic powers,” nonetheless, “these problems are not exclusive to naturalism.”
• James Van Cleve suggests that even if the probability thesis is true, this need not deliver an undefeated defeater to R, and that even if one has a defeater for R, why does it follow that one has a defeater for everything?
• Richard Otte thinks the argument “ignores other information we have that would make R likely”
• William Talbott suggests that “Plantinga has misunderstood the role of undercutting defeaters in reasoning,”
• Trenton Merricks says that “in general, inferences from low or inscrutable conditional probability to defeat are unjustified,”
• William Alston argues that the claim that P(R/N&E) is low is poorly supported; if, instead, it is inscrutable, this has no clear relevance to the claim that (1) is a defeater for N&E.

Fitelson and Sober (1998)

Branden Fitelson of the University of California, Berkeley and Elliott Sober of the University of Wisconsin-Madison criticised the argument in 1998 suggesting that Plantinga's argument merely shows that both traditional theism and naturalism are fallible They criticise his use of a Bayesian framework, and suggest that it would apply equally well to "any non-deterministic theory in the natural sciences" and other aspects of his use of probability is flawed in other respects. They also criticise Plantinga's presentation of the mechanisms of evolution and his analysis of the relation between belief and behavior. Plantinga may be correct that natural selection does not "care" about the truth or falsity of beliefs, but only behavior, but it does not follow that true and false beliefs are equally likely to evolve.

Finally, they suggest that Plantinga's argument does not show that proponents of metaphysical naturalism should a priori doubt all of their beliefs. This is because Plantinga's argument rests in part on the idea that E&N defeat proposition R (i.e., that evolution combined with naturalism make it unlikely that "the great bulk" of the beliefs that humans have are true). Plantinga draws from this defeat the notion that proponents of E&N should not have confidence in any of their beliefs, including their belief in E&N. But they suggest that "Even if E&N defeats the claim that 'at least 90% of our beliefs are true,' it does not follow that E&N also defeats the more modest claim that 'at least 50% of our beliefs are true'."

Plantinga's reply

Plantinga replies at length to "Beilby's cohorts" and to some objections raised by others, including Filetson & Sober, in sections as follows:

• He expounds the notion of Rationality Defeaters in terms of his theory of warrant and proper function and distinguishes between Humean Defeaters and Purely Alethic Defeaters, suggesting that although a Naturalist will continue to assume R "but (if he reflects on the matter) he will also think, sadly enough, that what he can't help believing is unlikely to be true
• He argues that Semantic epiphenomenalism is very likely on N&E because if materialism is true beliefs would have to be neurophysiological events whose propostional content cannot plausibly enter the causal chain. He also suggests that the reliability of a cognitive process requires the truth of a substantial proportion of the beliefs it produces, and that a process which delivered beliefs whose probability of truth was in the neighbourhood of 0.5 would have a vanishingly unlikely chance of producing (say) 1000 beliefs 75% of which were true.
• The conditionalisation problem
• Reply to Talbott
• To Bergmann
• To O'Connor
• To Van Cleve
• To Sosa
• To Merricks
• To Fodor
• To Ramsey
• To Fales
• To Otte
• To Alston

Further Discussion

Many modern philosophers of science, including atheists, use the term methodological naturalism to refer to the long standing convention that science uses a methodological assumption that the observable events in nature are explained by natural causes - without assuming the ontological existence or non-existence of the supernatural. Supernatural explanations for events would be outside science, but would not be necessarily inexistent or wrong. They contrast this with the metaphysical belief that the natural world (including the universe) is all that exists, and therefore nothing supernatural exists. Among other things, the distinction means that science does not deal with the question of the existence of a Creator, and argues neither for nor against it.

See also

• Conflict thesis

External links

• Plantinga's paper: "Naturalism Defeated" (pdf)
• Naturalism Defeated? reviewed by John F. Post at Notre Dame Philosophical Reviews