Evidence · Case 08 · Science

Plantinga’s argument, stated as a syllogism

One exhibit from the free evidence repository at apologetics.pro.

Let R stand for our thinking faculties are reliable, N for naturalism, and E for unguided evolution. Plantinga’s own form runs like this. One, the probability of R given N and E is low or unknowable, because evolution selects for useful behavior, not true belief. Two, anyone who sees this has a reason to doubt R. Three, a reason to doubt R is a reason to doubt everything those faculties produce, including N and E themselves. Four, a view that undercuts itself cannot be rationally held. Therefore naturalism joined to unguided evolution cannot be rationally affirmed. The target is that combination, not evolution on its own, since a theist can hold that God intended reliable minds.

Sources

Alvin Plantinga, “Where the Conflict Really Lies” (opens in a new tab)
Alvin Plantinga, “Where the Conflict Really Lies: Science, Religion, and Naturalism” (Oxford University Press, 2011)

Objections & responses

Step 3, that a reason to doubt reliability is a reason to doubt everything, is too strong. We can doubt our faculties in abstract metaphysics while trusting them in perception and survival-relevant reasoning, where selection pressure clearly applied.: This is one of the better responses in the literature. The reply is that the argument for naturalism itself is abstract metaphysics, so the domain restriction would undermine naturalism specifically while leaving everyday reasoning intact, which is close to the conclusion Plantinga wants. Whether faculties can be trusted domain by domain in this way is a fair question, and it is one you should weigh rather than take on trust from either side.
The argument proves too much. If unguided evolution undermines trust in reason, it undermines the theist’s reason too, since theistic evolutionists accept the same evolutionary history.: The argument targets naturalism plus evolution, not evolution alone, because a theist can hold that reliable minds were intended. The fair follow-up is that guided evolution is an unfalsifiable add-on, and that is partly right; but the argument is not offered as evidence for God. It is offered as a problem for one specific combination of views. A theist who accepts evolution has a reason to expect reliable cognition; a naturalist has to derive it from selection pressures alone, and that derivation is the step in dispute.
Plantinga’s probability claims are hand-waving. He never gives a principled way to estimate them, and his examples of adaptive false beliefs (the man who wants to be eaten by tigers) are contrived.: The tiger example is contrived, and even Plantinga’s defenders often drop it. The stronger form of the argument does not need it. It observes that selection acts on behavior, that many behavior-producing belief systems could be adaptive, and that we have no independent way to know ours is the truth-tracking one if naturalism is true. The critics’ reply, that true beliefs are generally more adaptive, is the crux, and it is presented as such in the next exhibit. This is the weakest argument on the site by its own admission, and it should be held that way.

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