QuestionsDoes God exist?If our reason comes from blind evolution, can we trust it?
Does God exist?TheismConsciousness

If our reason comes from blind evolution, can we trust it?

The evolutionary argument against naturalism

Alvin Plantinga born 1932Belief in God can be rational without proof, and evil does not make it incoherent.
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What it claims

Whoever believes in naturalism (and sees this argument) cannot rationally believe it: naturalism, joined to evolution, defeats itself.

Why

Unguided evolution keeps what helps us survive, not what is true: our faculties would then be unreliable.

The same idea through history
Charles Darwin1881In a letter to William Graham, he admits a "horrid doubt": can a human mind descended from that of animals be trusted? He applies this doubt to his own conviction that the universe is not the result of chance; Plantinga will extend it to all our beliefs.
C. S. Lewis1947In Miracles (ch. III), he argues that if all our thoughts have non-rational causes, naturalism destroys itself: it would be "a proof that there are no such things as proofs". After Elizabeth Anscombe's criticism, he rewrites the chapter in 1960.
Alvin Plantinga1993Last chapter of Warrant and Proper Function: naturalism joined to evolution gives whoever accepts it a reason to doubt their own faculties, and so this very naturalism.
Alvin Plantinga1994In "Naturalism Defeated", he clarifies the notion of a "defeater" (a reason to doubt) and answers the first objections.
Alvin Plantinga2011In Where the Conflict Really Lies (ch. 10), he targets materialist naturalism: even if a belief acts through the brain, selection does not see whether its content is true. The real conflict, he says, sets science against naturalism, not against religion.
In short

"If our reason comes from blind evolution, can we trust it?" is an argument by Alvin Plantinga (Warrant and Proper Function, 1993; "Naturalism Defeated", 1994, 1993) on the question "Does God exist?" (answer: theism). Its claim: Whoever believes in naturalism (and sees this argument) cannot rationally believe it: naturalism, joined to evolution, defeats itself. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P7). AskPhilosophy presents 4 objections, 3 of them with a documented reply, and the original text behind each premise, checked word for word.

Warrant and Proper Function, 1993; "Naturalism Defeated", 1994
Valid with an implicit premise

Naturalism says that only nature exists: no God, nothing supernatural. Our faculties (perception, memory, reasoning) then come only from evolution, with no one guiding it. Yet natural selection keeps what helps to survive and reproduce, not necessarily what is true. The American philosopher Alvin Plantinga draws a surprising consequence: the naturalist who thinks about this no longer has good reason to trust their own reason, and so not their belief in naturalism either. On his view, naturalism saws off the branch it sits on. The argument does not prove that God exists. It targets naturalism, and it sides with theism because the believer thinks our faculties were made to know the truth. The idea has a history: Darwin had suspected it, and C. S. Lewis had turned it into an argument in 1947.

P1If naturalism is true, our cognitive faculties come only from evolution, with no guide at all. For the naturalist, evolution is the only explanation available.
P2Unguided evolution only keeps behaviour useful for survival and reproduction. It cares about the truth of our beliefs only insofar as they make us act.
P3So, for whoever accepts naturalism and evolution, the probability that our faculties are reliable (that they mostly produce true beliefs) is low, or impossible to assess. This is "Darwin's doubt".
P4Believing that the reliability of one's faculties is improbable, or impossible to assess, given their origin, gives a reason to doubt that reliability (a "defeater"). It is like believing one may have been made by a deceiving demon.
P5This doubt cannot be removed by reasoning: any reasoning meant to prove that our faculties are reliable would use those very faculties, and so assume what it wants to prove.
P6A reason to doubt one's faculties that cannot be removed holds for each belief they produce: one can no longer rationally accept any of these beliefs.
P7 · implicit premiseBelief in naturalism is itself produced by these ordinary faculties (observation, reasoning), and not by some other source safe from the doubt.
Therefore whoever believes in naturalism (and sees this argument) cannot rationally believe it: naturalism, joined to evolution, defeats itself.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P7, the computer finds a world where the naturalist does have a reason to doubt all their ordinary faculties, but holds naturalism from some other source, safe from this doubt. They could then rationally believe it.
Valid with P7, which the argument leaves unstated because it seems obvious: the naturalist does not hold their doctrine from a revelation, but from observation and reasoning. The debate is mostly about P2 (does selection not favour truth as well?), P3 (is the probability really low?) and P4 (is ignorance of a probability a reason to doubt?). Note: the conclusion targets naturalism, not evolution. Plantinga accepts evolution, but an evolution that God can guide.
Analogy. You are told that you unknowingly swallowed a pill that disrupts the reasoning of one person in two, and that you feel nothing. You want to check whether your mind still works: but to check, you must reason, with the possibly disrupted mind. For Plantinga, the naturalist is in this position: their own theory tells them their mind was not made for truth.

Objections

4

Each objection is a conversation: click to see who replies and where the debate stands.

Elizabeth Anscombe (against Lewis's version) 1948 · attacks premise 4

At the Oxford Socratic Club, the philosopher Elizabeth Anscombe answers Lewis. He confuses "irrational" (contrary to reason, like a delirium) and "non-rational" (merely physical). That a thought has physical causes does not prove it is badly reasoned. And validity is a quality of arguments, not of their causes: to judge an argument, we examine it, we do not look for where it came from. Explaining a thought by its causes and justifying it by reasons are two different questions.

Plantinga replies
C. S. Lewis 1960
Lewis rewrites the chapter for the new edition of Miracles, under another title: "The Cardinal Difficulty of Naturalism". He distinguishes two senses of "because": cause and effect (one fact produces another) and ground and consequent (one idea justifies another). For a thought to be knowledge, it must be produced by our seeing the ground. Yet naturalism explains our thoughts only by causes and effects.
The debate goes on (our summary) Lewis does not keep his first formulation: he restates it more carefully, which shows the criticism hit home. The debate went on. Victor Reppert (C. S. Lewis's Dangerous Idea, 2003) defends a renewed form of the argument. His critics answer that computers show a purely physical process can follow the rules of logic. Plantinga changes ground: he no longer asks whether a thought with causes can be rational, but whether faculties produced without guidance are likely to aim at truth.
W
William Ramsey 2002 · attacks premise 2

Truth is no luxury for survival. According to "evolutionary reliabilism", our cognitive mechanisms are useful partly because they produce desires (to stay alive, to reproduce) and accurate representations of the world, which let the animal get around and satisfy those desires. The truth of our beliefs therefore partly explains why they are useful: selection may have favoured it.

Plantinga replies
Alvin Plantinga 2002
In his reply to the authors of the same volume, Plantinga grants that truth is a property that depends on a relation to the world. But for him, that is not the question: what matters is whether a belief acts on behaviour by way of its content, that is, by what it says.
The debate goes on (our summary) Plantinga develops this point in 2011 (Where the Conflict Really Lies, ch. 10). If naturalism is materialist, a belief is a structure in the brain. This structure makes us act through its physical properties, and selection keeps its effects. But nothing guarantees that the content carried by this structure is true: the probability that a given belief is true would be about one in two. Many naturalists answer that the content of a belief is not stuck onto the brain at random. It depends partly on the role the belief plays in action and in the link with the world (this is the idea of "teleosemantics", put forward notably by Ruth Millikan). A belief that guides action well would then tend to be true. The debate remains open.
B
Branden Fitelson and Elliott Sober 1998 · attacks premise 4

Not knowing how to assess a probability is no reason to doubt. Many people who know relativity and know that birds fly do not know what probability to give relativity given that birds fly: they need not give up relativity for that. Making our ignorance a guide to belief is a mistake. And the theist is no better off: faced with radical doubt about all our faculties, neither he nor the naturalist has an argument that does not already assume what is in question. The right lesson of evolution is humility: our theories are fallible, and we must do our best with the mind we have.

Plantinga replies
Alvin Plantinga 2003
In "Probability and Defeaters", Plantinga answers that his argument does not say that every unknown probability gives a reason to doubt. The doubt arises in a precise case: when what one oneself believes about the origin of one's faculties makes their reliability improbable or impossible to assess, as for someone who considers having been made by a deceiving demon.
The debate goes on (our summary) On the second point (the theist is no better off), Plantinga's defenders answer that he does not claim to refute radical doubt. He only says that the theist, who believes himself made in God's image, has no particular reason to doubt his faculties, whereas the naturalist receives one from his own worldview. His critics answer that one can keep ordinary trust in one's faculties without grounding it on a story of their origins. The debate on the notion of a "defeater" remains technical and open.
J
Jerry Fodor 1998 · attacks premise 3

Fodor grants part of the starting point: evolution does not guarantee that most of our beliefs are true, and he warns against those who too quickly conclude the opposite. But nothing in evolutionary theory suggests that our beliefs, and science, are unreliable. The most Plantinga gets is that evolution is compatible with science being unreliable. That is true, but not interesting: "the cat is on the mat" is also compatible with it.

no reply
We have not yet found a direct reply by Plantinga in the texts.
The debate goes on (our summary) Plantinga's defenders answer that his argument does not need evolution to make our beliefs probably false. It is enough that the probability of their reliability be impossible to assess, and Fodor's concession (evolution does not guarantee truth) leaves this possibility open. Fodor judges on the contrary that without a positive reason to doubt, nothing forces us to give up ordinary trust in science.
What today's voices say
Defend it
John LennoxHis main reply to atheism: if our thoughts are only the by-product of mindless processes, why trust them? 'Atheism is irrational because it tries to derive rationality out of irrationality.'
Wesley HuffIf thought is only chemicals and chance, he asks, why trust our reasoning at all?
Bishop Robert BarronHe finds Lewis's argument from reason convincing for higher abstract reasoning, less so for ordinary brain function.
Frank TurekHe argues that if we are only 'moist robots', we cannot trust our reasoning, atheism included. He reads C.S. Lewis: 'unless I believe in God, I can't believe in thought'.
In the same family · Consciousness
Where does consciousness come from? From the physical you only get the physicalJ. P. Moreland · 1998 · debate over 3 levels
Does God exist?Theism 5