Type-Physicalism, Functionalism, and Eliminative Materialism

Type Physicalism (The Identity Theory or Type Identity Theory)

The Type Physicalist, called by Churchland the "Identity Theorist", is committed to the view that any mental state of a certain type is a brain state of a certain type.

For example, the mental state of feeling pain is the brain state of c-fiber nerve firing. In short, pains are brain states.

Recall that one of the more serious problems for Cartesian Dualism is explaining just how two different substances, mind and body, causally interact. Type Physicalism neatly solves this problem by holding that every kind of mental event is a type of physical event.

But is that true?

Type Physicalism is excessively anthropocentric. It implies that only creatures with our particular neurophysiological make-up could have mental states like ours. A martian, for example, could not have pains unless it had c-fiber nerve firings, which it could not have if it had no c-fiber nerves.

Functionalism

What sort of thing would a mental state have to be so that creatures having distinct neurophysiological make-ups could have the same mental state?

Consider the following analogy:

Clocks tell time. That is their function. Yet a clock may be made out of wood (as they were several hundred years ago), they may use water (as in old-time water clocks), they may use sand (hour glasses can still be had as kitchen timers), they may be made out of metal, or they may not have any moving parts at all. Thus the function of telling the time is multiply realizable: there are many different ways to implement the function of telling time.

Now consider a slightly more sophisticated analogy:

The computer has the capacity run different programs. Moreover, a single program can be run on computers that are completely different in design. For example, the wordprocessor I am using to write this, LibreOffice, can run on both Macintoshes and PC's. Yet the program, and all of the functions associated with the program, is the same whatever the platform.

Perhaps, then, the brain is the platform of the mind, so creatures with completely different brains may have have the same mental states. Hence the mental states are not (type) identical to physical states. Rather, mental states are functional states. The mind is to the body as software is to the CPU. Pain is not a physical state; it is a functional state.

The Absent Qualia Objection

Suppose that all of the functional roles played by mental states are replaced by individual homunculi--little 'men' in the head who read an input from other little men and give an output. In principle, the homunculized person will be indistinguishable from the original, non-homunculized person, if either Machine or Analytic Functionalism is true. Yet the homunculized person lacks qualia--the raw feels or the 'what it is like to experience x'. Thus not every metal state is individuated by its functional role, so Functionalism is false.

The Inverted Qualia Objection

What if what you perceived as red is what I perceived as green, and what you perceived as green I perceived as red? You would call the green apple "green", of course, because you were taught to do so. Yet if I could have your experience of the green apple, I would say that it is a red apple.

This is possible. It may even be a real phenomenon, if modern neurophysiology is correct. We'll never know for sure, and therein lies the challenge to functionalism. You and I behave no differently. When asked to get a green apple, we both head for the green apples. The functional roles of our mental states are the same. Nevertheless, the associated qualia of what it is like to experience a green apple is radically different. Thus mental states are not individuated by their functional role, so Functionalism is false.

These are serious challenges to both Machine and Analytic Functionalism. It is not clear how or even whether the Functionalist can respond.

Eliminative Materialism

A more radical alternative to both Type Physicalism and Functionalism is Churchland's Eliminative Materialism. The idea behind Eliminative Materialism is that, historically, some explanations have been rejected in favor of other explanations. For example, it was once thought that fire always involved a special substance called "phlogiston". Phlogiston was used to explain how a fire started, spread, and died. "Phlogiston" was eliminated from the physicists vocabulary, however, when it was discovered that all the facts about fire could be explained without any mention of phlogiston. Similarly for Eliminative Materialism, the ordinary folk-psychological explanations we give for someone's actions in terms of their beliefs, desires, and intentions will be eliminated by a mature psychology (specifically, a mature neuropsychology).