Over the past century there have been several paradigms or patterns of explanation by which philosophers and neuroscientists have tried to understand the mind.

Behaviorism was the view that the input to and output from the nervous system was all that mattered. The ‘mind’ was deemed irrelevant to science. Behaviorism was eclipsed by reality—it was more or less demolished in the 1960’s by Noam Chomsky (1928–), who pointed out that language could not be understood in behaviorist terms. The study of the mind is indispensable to linguistics, neuroscience and philosophy. That this needed to be said is a scandal in itself.

Identity theory — the view that mental states are identical to brain states — was the rage for several decades, until it was acknowledged that in order to be identical, mind states would have to be the same as brain states, which they aren’t.

Eliminative materialism — the belief that the mind does not exist — has had a run for a couple of decades as well. Materialists acknowledged that they had no material explanation for the mind. But rather than jettison materialism, they jettisoned the mind. I predict that eliminative materialism will have a short shelf life, as more effective psychiatric care becomes available.

The theory that survived all of this debate seems to be functionalism. Functionalism is the view that what makes something a mental state is the role it plays — its function — in a cognitive system. Functionalism is often explained colloquially as “the mind is what the brain does.”

Functionalism bears a superficial resemblance to the Aristotelian understanding of the soul, which is one of its strengths. Aristotle said the soul is the active principle—the powers, so to speak—of a human being. Colloquially, we might say the Aristotelian view is that the mind is the spectrum of cognitive abilities of a human being. Aristotelian psychology* makes sense and corresponds well with the results of modern neuroscience. I think it is the best understanding we have of the mind.

Functionalism differs, however, from Aristotelian psychology and the differences are fatal for the functionalist understanding of the mind. There are two major reasons functionalism fails.

1.Functionalist theories generally describe mental states as functions of brain states, rather then as functions of human beings as a whole. This is the mereological fallacy—the erroneous attribution of powers of the whole to its parts. Only human beings see, hear, remember, understand, and will. Brains do brain things—generate action potentials, secrete neurotransmitters, metabolize glucose, etc.

It simply makes no sense to say that brains think, so the assertion that “the mind is what the brain does” is not merely wrong. It is, literally, nonsense, analogous to saying that feet run (ignoring the rest of the body) or that the ability to smell is a square root. It’s gibberish.

2.The most common version of functionalism is computer functionalism. Computer functionalism is the assertion that the brain and mind are a form of computation such that the brain and the mind bear the relation of hardware to software. This is also nonsense — the brain is not a computer and the mind is not a computation. The brain can be studied using computational models, but to call the brain a computer is just nonsense. Voting patterns can be studied using computational models but that doesn’t mean that voters are computers.

The most egregious error in computer functionalism (as if being nonsensical were not egregious enough) is the assertion that the mind is a kind of computation. Computation is the algorithmic matching of an input to an output. The hallmark of computation is that it is blind to meaning — that is, it matches signal to signal, regardless of the semantic content of the signal. A word processing program works just as well for an essay expressing a “yea” opinion as it does for an essay expressing a “nay” opinion. Computation is blind to meaning.

Mental states, on the other hand, always have meaning. That is, thoughts always point to an object — to a tree perceived, or to a person loved, to a concept understood or a goal pursued.

Not only is it untrue to say that the mind is computation but the mind is the opposite of computation. Computation always lacks meaning and the mind always has meaning. The computer functionalist couldn’t be more wrong.

As I noted, I have some sympathy for functionalism because, although it is deeply flawed, it is an effort to explain the mind as abilities, which is a good start toward genuine insight. But there’s no reason to embrace functionalism when there is a much more acceptable and profound theory of mind — Aristotle’s clear and cogent view that mental states are the cognitive powers of a human being — is on tap.

• Philosopher Edward Feser has a nice synopsis of Aristotelian–Thomistic psychology in chapter 4 of his superb book Aquinas.

You may also enjoy this article by Michael Egnor: A reader asks: Does neuroscience disprove free will? Materialists sometimes misrepresent the evidence for free will, especially Benjamin Libet’s work. We most certainly do have free will. We can see this from three perspectives: scientific, philosophical and logical.