[I have written about this before, but wanted to get a version of it in my blog.]
For some hundreds of years Western thought has been rationalistic, claiming that the touchstone of truth is reason. A rational thought follows the laws of reason, and has the property that it is truth-preserving. By this I mean the following.
Say we take a simple rational inference:
All men are mortal
Socrates is a man
Socrates is mortal
In more general form we can express this as
All A are B
C is A
C is B
Or even more abstractly we can say
A –> B
C –> A
C –> B
where “–>” can be read “implies.”
The first two expressions are called “premises” and the third is called the “conclusion.”
In a rational thought the truth of the premises guarantees the truth of the conclusion.
Now if we take the following set of expressions we notice something interesting.
A –> B
C –> B
C –> A
Trying this out with poor Socrates, we get the following:
All men are mortal
Socrates is mortal
Socrates is a man
My cat Socrates objects strenuously to this conclusion. (Actually I don’t have a cat, but if I did, and if he were named Socrates, he would probably scratch me, mortal though he be.)
Now it’s pretty easy to see that the second example of reasoning is incorrect, because it’s easy to find counterexamples. However, in the first example, can we be certain that this manner of reasoning will always yield truth? What is better about the first example than the second? When we think the thoughts represented by the second example, and the thoughts represented by the first example, they are both thoughts. How do we distinguish between them?
This question has perplexed believers in naturalistic evolution since Darwin, who asked the question of whether one could believe the convictions of a mind that has developed from the mind of lower animals.
Stephen Hawking, in his book A BRIEF HISTORY OF TIME, wrote the following:
Now, if you believe that the universe is not arbitrary, but is governed by definite laws, you ultimately have to combine the partial theories into a complete unified theory that will describe everything in the universe. But there is a fundamental paradox in the search for such a complete unified theory. The ideas about scientific theories outlined above assume we are rational beings who are free to observe the universe as we want and to draw logical deductions from what we see.
In such a scheme it is reasonable to suppose that we might progress ever closer toward the laws that govern our universe. Yet if there really is a complete unified theory, it would also presumably determine our actions. And so the theory itself would determine the outcome of our search for it! And why should it determine that we come to the right conclusions from the evidence? Might it not equally well determine that we draw the wrong conclusion? Or no conclusion at all?
This poses the problem at a lower level than even Darwin — if the theory of everything explains everything we do, then even our belief in the theory of everything would be caused by physical laws and not by the truth of the theory.
Ironically, Hawking appeals to Darwin, giving the following resolution of the paradox:
The only answer that I can give to this problem is based on Darwin’s principle of natural selection. The idea is that in any population of self-reproducing organisms, there will be variations in the genetic material and upbringing that different individuals have. These differences will mean that some individuals are better able than others to draw the right conclusions about the world around them and to act accordingly. These individuals will be more likely to survive and reproduce and so their pattern of behavior and thought will come to dominate. It has certainly been true in the past that what we call intelligence and scientific discovery have conveyed a survival advantage. It is not so clear that this is still the case: our scientific discoveries may well destroy us all, and even if they don’t, a complete unified theory may not make much difference to our chances of survival. However, provided the universe has evolved in a regular way, we might expect that the reasoning abilities that natural selection has given us would be valid also in our search for a complete unified theory, and so would not lead us to the wrong conclusions.
The problem with this argument, of course, is that it is circular. Since evolution and natural selection are parts of any theory of everything, then by appealing to natural selection to justify the theory of everything, you are actually appealing to the theory of everything to justify itself. Christians are rightly taken to task for saying that the Bible is true because the Bible says it is true. But this is a similar kind of argument.
Hawking is actually assuming that “drawing right conclusions about the world around them” is necessarily connected with surviving and reproduction. But naturalistic evolution only says that organisms survive by being better adapted (in some unspecified way) to their environment. This has no necessary connection with “drawing right conclusions” and therefore no reason to believe that natural selection will “not lead us to the wrong conclusions.”
The problem is that in my example above, both the first and second example can be said to be the result of natural selection. Why is the first guaranteed to give a true conclusion, while the second is not? All naturalistic evolution tells us is that both thoughts are the result of beings that survived. But we are looking for something that tells us that one thought is true, while the other is fallacious.
Note that we do think like this, and it does work for us to an amazing extent. Einstein is famous for saying that the most incomprehensible thing about the universe is that it is comprehensible. There is a famous paper called The Unreasonable Effectiveness of Mathematics in the Natural Sciences that makes this point. (I would recommend that everyone read the first paragraph of this paper; it puts the point humorously.)
On this basis we might be suspicious that there is something more than random chance and natural selection involved; perhaps we are somehow able to tap into some higher faculty for truth-telling. At the very least, we act as if that were true.
Consider the alternative. Someone makes a rational argument, and we dismiss it by saying, “You are saying that because natural selection acting on random events caused you to say it.” Would not this be the height of unreason? And yet if naturalism is true what more can we say?
There are numerous instances of this argument given on the internet. Here is one.
C. S. Lewis gave this argument in his book Miracles in the chapter called The Cardinal Difficulty of Naturalism.