In The Immortal Mind that I have co-authored with Denyse O’Leary, we provide detailed neuroscientific reasons why the human capacity for abstract thought — which is the intellect — is an immaterial power of the human mind.

But there are also logical reasons for thinking that the intellect is immaterial, which means spiritual. Consider, for example, our capacity to think abstractly, without finite bounds.

Are all mind states brain states?

The materialist view is that the entire mind, intellect, perception, memory, etc., is wholly a physical product of the brain in one way or another. That is to say, all mind states are brain states.

That claim is likely true for some mind states. Consider perceptions like vision. When I look at a scene, my vision is mediated by photons striking my retinal cells. I have a finite number of retinal cells (about 96 million rod and cone cells). This puts a limit on the resolution of my vision. Also, my vision is only sensitive to certain wavelengths of light — I can only see visible light, not infrared or ultraviolet light. Vision is amazing, but it is not infinite.

But now consider my intellect. There is no similar finite bound on the size of a number I can contemplate. I can think of the number 7×10^27, which is 7 octillion. That is roughly the number of atoms in the universe. But I can also easily think of twice that number —1.4×10^28, and then double that number. How about an octillion times 7 octillion. There is no limit on the numbers I can think of.

So the question for materialists is this: how can the infinite capacity of my intellect, which is my capacity for abstract thought, be generated by a finite number of neurons or atoms in my brain? How can infinite states of my intellect be generated by finite states of my brain?

The limits of brain states

Neuroscience shows that while movement, perception, emotion, and memory arise from brain states, intellect and free will do not. Normal brain function is necessary for abstract thought, but brain states alone are insufficient for it. Both neuroscience and logic support the conclusion that the intellect is an immaterial power of the human mind.