The most pervasive myth in neuroscience and philosophy of mind is that the mind is wholly generated by the brain.

No question, many of the things we experience are closely linked to brain function. Physiological processes like heart rate control, breathing, blood pressure, hormones, etc., are tightly linked to it. Movement, perception, memory, emotion, and imagination are also tightly linked to brain function. We can consider them to be caused by the brain.

Two mental powers that are not caused by the brain

Those two powers are intellect and will. In general, intellect refers to the capacity to think abstractly about concepts instead of specific objects. It is the ability to reason, use judgment, have concepts, and use logic and language. For example, emotion may prompt a lonely man to think about adopting a puppy. Reason bids him to think about the responsibility he is taking on for, perhaps, fifteen years.

Will is the ability to choose based on reason. In this sense, will follows on intellect. The intellect is directed to knowing truth. The will is directed to seeking good. A properly functioning will should prompt the man to make a decision based on what is best for the dog as well as for himself, not merely on the emotion he is feeling as he cuddles the dog at the pet adoption center.

The intellect tells the will (so to speak) what is good, and the will pursues it. While normal brain function is necessary for the normal exercise of intellect and will, brain function is not sufficient for them. Your intellect and will are immaterial—i.e., spiritual—powers of your soul.

How we know that abstract thought is not material

I have written about the massive evidence from neuroscience that intellect and will are immaterial powers of the mind—here, here, here, here, and here. There is powerful evidence from logic for immateriality of the intellect as well—today we’ll discuss the argument from indeterminacy of matter.

This argument for the immateriality of the intellect dates back to Plato (c. 427 – 348 BC) and Aristotle (384– 322 BC). It has been advocated by many modern philosophers too, most notably James Ross and Edward Feser. Succinctly, it goes like this:

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1. Abstract thought can have exact and unambiguous conceptual content.
2. Nothing material can have exact and unambiguous conceptual content.
3. Therefore, abstract thought is not material.

By using our intellect we can think about exact things. But no material state of the brain can be exact. There is always a measurable level of uncertainty in any material state.

That uncertainty originates right down at the quantum level—the behavior of the elementary particles that make up our physical universe. It is expressed in Heisenberg’s uncertainty principle. The principle states that pairs of measurements (such as position and momentum, or energy and time) can never be known simultaneously with certainty, not even in theory.

Even in our own, much larger, size range, we experience the effect of that fundamental uncertainty. For example, our vision is pixelated because photons activate individual retinal cells. So there are built-in limits to its precision.

Recognizing that indeterminacy is a fundamental fact about matter helps us see the difference between abstract concepts, which can be precise—like the number 7—and material states of the brain, which never are.

Why our concepts can be precise

Concepts, because they are not material, don’t share the inherent uncertainty that is characteristic of matter. Consider our concept of a point in geometry. We conceive of a point as a location with no dimensions and no qualities such as color, shape, etc. Yet every point we see and every point we imagine by means of a picture in our mind has dimensions and attributes like shape and color. Those dimensions and attributes are more or less inexact and indeterminate.

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All lines we conceive of abstractly in our intellect are exactly straight—the shortest distance between two points. Yet no physical line we have ever seen is exactly straight.

Similarly, our abstract concept of a triangle is exact: a closed three-sided plane figure with internal angles that add to 180 degrees. But no material triangle—not a triangle drawn on paper or on a white board or represented in a brain state—is ever exact.

Exact thought cannot logically be generated by inexact brain matter.*

What do materialists say about this?

Materialists counter that our abstract concepts aren’t really exact. They are just very close approximations. But that’s obviously not true—our concepts of geometrical figures or logic itself are genuinely exact. It is matter that is never exact. In fact, the materialist invocation of logic to make their arguments presupposes the precision of logic. If the materialist’s own viewpoint couldn’t be precisely true, it wouldn’t be valid.

The indeterminacy of matter precludes brain states from forming the basis of abstract thought. In addition to the massive evidence from neuroscience that the intellect is an immaterial power of the mind, simple logic points to the same truth.

*For readers who are interested in a deeper dive into these issues, my co-author Denyse O’Leary and I discuss all of this evidence in our new book The Immortal Mind: A Neurosurgeon’s Case for the Existence of the Soul (June 3, 2025)I also recommend Ed Feser’s book Immortal Souls: A Treatise on Human Nature(2024)which is a superb exploration of these philosophical issues.