If matter, energy, and physical forces like gravity are all there is then everything is ultimately reducible to material, non-rational particles. If so, our beliefs are just brain states that can be completely explained in terms of non-rational chemical reactions, but any belief that is fully explicable in terms of non-rational causes cannot itself be rational.
Therefore, if materialism is true, none of our beliefs are rational, reason itself is a non-rational illusion, and both truth and the reliability of scientific investigation are chimerical. Thus the atheistic materialist has no rational basis for believing that materialism, or anything else, is true.
As Stephen Pinker of MIT has said, "Our brains were shaped [by evolution] for fitness, not for truth." Only if our reason is an endowment from an omniscient, good Creator do we have actual warrant for placing confidence in it. We may, if we don't believe that there is a Creator, decide to trust reason simply as an act of faith, but it's very difficult to justify the decision to do so since any justification must itself rely upon rational argument. And, of course, employing reason to argue on behalf of its own trustworthiness begs the question.
Philosopher Alvin Plantinga, in his book Where the Conflict really Lies, presents a defeater for the belief that both naturalism and evolution (N&E) are true.
Philosopher William Lane Craig summarizes Plantinga's argument as follows:
1. The probability that our cognitive faculties are reliable, given naturalism and evolution, is low.Premise #1 is based on the fact that if our cognitive faculties have evolved then they have evolved for survival, not for discerning truth. This is not a fringe idea. It's admitted on all sides by atheists and theists alike. The quote from Steven Pinker above is an example and here are a few more among the many that could be cited:
2. If someone believes in naturalism and evolution and sees that, therefore, the probability of his cognitive faculties’ being reliable is low, then he has a defeater for the belief that his cognitive faculties are reliable.
3. If someone has a defeater for the belief that his cognitive faculties are reliable, then he has a defeater for any belief produced by his cognitive faculties (including his belief in naturalism and evolution).
4. Therefore, if someone believes in naturalism and evolution and sees that, therefore, the probability of his cognitive faculties’ being reliable is low, then he has a defeater for his belief in naturalism and evolution.
Conclusion: Naturalism and evolution cannot both be rationally accepted. If one is true the other must be false.
Evolution selects for survival and “Truth, whatever that is, definitely takes the hindmost.” - Atheist philosopher Patricia Churchland.Oddly none of these thinkers carried their idea to its logical conclusion, but the theist C.S. Lewis does it for them in his book On Miracles where he writes:
Modern [naturalism] is the faith that through science humankind can know the truth and so be free. But if Darwin's theory of natural selection is true this is impossible. The human mind serves evolutionary success, not truth. - Atheist philosopher John Gray
Our highly developed brains, after all, were not evolved under the pressure of discovering scientific truths but only to enable us to be clever enough to survive.- Atheist biologist Francis Crick
Supposing there was no intelligence behind the universe, no Creative Mind. In that case, nobody designed my brain for the purpose of thinking. It is merely that when atoms inside my skull happen, for physical or chemical reasons, to arrange themselves in a certain way, this gives me, as a by-product, the sensation I call thought.If theism is true then, of course, the evolution of our cognitive faculties could be goal-directed by God toward discovering truth, but that possibility isn't open to the naturalist since she doesn't believe theism is true.
But, if so, how can I trust my own thinking to be true?.... Unless I believe in God, I cannot believe in thought: so I can never use thought to disbelieve in God.
Thus, the argument outlined above leads to the conclusion that it can't be rational to believe in both N&E. This is bad enough for the naturalist, but it gets worse, as Craig points out.
The naturalist is faced with a defeater for any belief that he holds since none of his beliefs are reliable. He can't believe that N&E are both true, nor can he believe that either one or both are false. On naturalism no belief, especially no metaphysical belief, is rational since our cognitive faculties are not reliably geared toward truth. If they happen to hit upon truth it's just a serendipitous outcome, and we can't even be rationally assured that we've hit upon the truth.
To loosely cite Craig again:
The naturalist is caught in a logical quagmire from which there is no escape by rational thought. He cannot even rationally conclude that he cannot rationally accept both naturalism and evolution and that he therefore ought to abandon naturalism. He can’t rationally conclude anything. He's caught in a circle from which there is no means of rational escape.And yet, despite all this, the naturalist accuses the theist of being irrational for believing in God. It'd be funny were it not so sad.
