Philosophy of Mind Part 3: Physicalism

The Core Claim

Physicalism (also called materialism) holds that everything that exists is physical — or, more carefully, that every entity, property, and process either is identical to a physical one or wholly depends on physical ones. Applied to mind: there are no spooky non-physical minds, souls, or mental substances; the mental is, ultimately, brain.

The motivation is overwhelming: every detailed thing we have learned about minds (perception, memory, mood, language, reasoning) maps onto neural structure and function. Lesion a brain region, lose the corresponding capacity. Stimulate it, evoke the experience. The pattern is universal. Dualism leaves these correlations as unexplained miracles. Physicalism explains them by identity.

Behaviorism — The First Wave

Two flavors arose almost simultaneously in the early 20th century. Methodological behaviorism (Watson, Skinner) was a research program: psychology should study only observable behavior, since "inner mental states" are unscientific. Logical behaviorism (Ryle, Carnap, the early Hempel) was a philosophical thesis: statements about mental states are analyzable into statements about behavioral dispositions.

To say "Smith believes it will rain" just is to say that Smith is disposed to take an umbrella, postpone the picnic, look at the sky. There is no extra inner fact.

Behaviorism collapsed. Chisholm showed that any analysis of belief into behavior secretly required other mental states (what Smith does with his belief depends on what he desires). Putnam noted that pain is not just a disposition to wince — Spartans trained not to wince still feel pain. The inner state had snuck back in.

Identity Theory

In the 1950s, Australian philosophers — U.T. Place ("Is Consciousness a Brain Process?", 1956) and J.J.C. Smart ("Sensations and Brain Processes", 1959), joined later by D.M. Armstrong — proposed a clean alternative: mental states are identical to brain states. Not analyzed-into-behavior; not correlated-with-brain; identical, in the same way that "water = H₂O" or "lightning = electrical discharge."

The identity is contingent and discovered empirically, not logical or definitional. Saying "pain = C-fiber firing" is no stranger than saying "the morning star = the evening star": we needed astronomy to discover the second; we need neuroscience for the first.

Type vs Token Identity

• Type identity: the type of mental state is identical to a type of brain state. Every instance of pain is C-fiber firing.
• Token identity: each instance of a mental state is identical to some brain state — but different instances may be different physical types. My pain might be C-fiber firing; an octopus's pain something else entirely.

Type identity faces a serious problem: multiple realizability. If pain is "by definition" C-fiber firing, then octopuses (with no C-fibers) cannot feel pain, and a hypothetical silicon alien cannot either. This struck most philosophers as wrong, and pushed them toward token identity or — more decisively — toward functionalism (Part 4).

Eliminative Materialism

Paul and Patricia Churchland took a more radical line. Folk psychology — our everyday talk of beliefs, desires, hopes, fears — is, they argued, a theory. Like phlogiston theory in chemistry or caloric theory of heat, it might simply be false. As neuroscience matures, we may not reduce folk-psychological kinds to neural ones; we may eliminate them, the way modern chemistry eliminated phlogiston.

If the Churchlands are right, future generations will not say "I believe it's raining" but something more accurate about the activation states of neural populations. The picture is dizzying — and resisted by most philosophers, since folk psychology seems to work for predicting behavior in a way phlogiston never did.

Nagel's Bat — The Subjective Standpoint

Thomas Nagel's 1974 paper "What Is It Like to Be a Bat?" is one of the most cited papers in philosophy of mind for a reason. Nagel argued: a conscious being has, by definition, "something it is like" to be it. There is something it is like to be you reading this sentence — a subjective character. There is presumably something it is like to be a bat using echolocation to hunt insects.

But no matter how completely we describe the bat's neurophysiology in objective, third-person terms, we can never capture what it is like to be the bat from the inside. Subjective character is perspectival — accessible only from one point of view — while physical description is essentially perspectiveless.

Mary's Room — The Knowledge Argument

Frank Jackson's 1982 thought experiment is even sharper. Imagine Mary, a brilliant neuroscientist who has lived her entire life in a black-and-white room. She has access to all physical information about color vision — every wavelength, every retinal mechanism, every cortical pathway, every behavioral correlation. She knows everything physical there is to know about red.

One day, Mary leaves the room and sees a ripe tomato for the first time. Does she learn something new?

The intuition is overwhelming: yes, of course she does. She learns what red looks like, the qualitative character of the experience. But she already had all the physical information. So there must be something — phenomenal character, qualia — that is not captured by the physical facts. Hence physicalism is false (or at least incomplete).