Let us suppose, unrealistically, that IQ tests really measure intellectual ability. Let us in fact assume, even more unrealistically, that they measure the intellectual abilities that are relevant to success in metaphysics. Why should we suppose that a species with a mean IQ of 100—our own species—is able to solve the problems of metaphysics? Pretty clearly a species with a mean IQ of 60 wouldn’t be in a position to achieve this. Pretty clearly, a species with a mean IQ of 160 would be in a better position than we to achieve this. Why should we suppose that the “cut-off-point” is something like 90 or 95? Why shouldn’t it be 130 or 170 or 250? The conclusion of this meditation on mystery is that if metaphysics does indeed present us with mysteries that we are incapable of penetrating, this fact is not itself mysterious. It is just what we should expect, given that we are convinced that beings only slightly less intellectually capable than ourselves would certainly be incapable of penetrating these mysteries. If we cannot know why there is anything at all, or why there should be rational beings, or how thought and feeling are possible, or how our conviction that we have free will could possibly be true, why should that astonish us? What reason have we, what reason could we possibly have, for thinking that our intellectual abilities are equal to the task of answering these questions?

Peter van Inwagen, Metaphysics, Boulder, Colorado, 1993, p. 201