NEIL W. TENNANT

tennant.9@osu.edu

If you email me, please use the header PHIL 101: [YOURNAME].

Professor
Department of Philosophy


Lecture summary © Neil Tennant, April 2002

Supervenience: the central notion for materialist philosophies of mind

Materialist philosophers of mind deny that minds are separate entities from bodies. But they insist that all mental events, states or processes are physical events, states or processes respectively. All that there is, is physical; but some of it is also mental, in the sense that it has mental attributes.

The priority of the physical is stressed by the materialist's supervenience thesis:

The mental supervenes on the physical.
That is, the physical facts (about all the individuals and stuffs in the universe) fix or determine whatever mental facts there may be, involving (some of) the individuals in question. Put another way: there could be no change in the mental state(s) of any individual without some corresponding change in its physical state(s).

Do not confuse the supervenience thesis with any thesis of determinism, to the effect that the future states of the world are fixed or determined by its present state. Determinism has to do with causality `all at the physical level', as it were. The present and future states mentioned in the determinist's claim can be thought of as exclusively physical states. Moreover, deterministic causation involves the lapse of time: the present state causes each later state to be what it is.

By contrast, the supervenience theorist's `fixing' or `determining' of the mental by the physical is a simultaneous fixing or determining. It has to do with synchronic relations between two levels of reality; causation is not involved. This is compatible with saying that some mental events have physical effects, and that some physical events have mental effects. Those sorts of claims would still be true, involving, as they do, the lapse of time. What the supervenience theorist is getting at, instead, with her talk of the physical fixing or determining the mental, is the synchronous metaphysical pinning down of one level of factuality by another.

The supervenience theorist is a materialist because of the order of determination chosen: it is the physical that fixes or determines the mental. Had it been the other way round, we would have been dealing with an idealist rather than a materialist! For the idealist metaphysician claims that the fundamental level of reality is that of ideas, and that material objects are at best constructions out of these. That is, for the idealist, it is the mental that would fix or determine the physical.

Philosophical materialism insists on an asymmetry between the mental and the physical. This asymmetry is underscored in three ways:

  1. Every mental event is a physical event. But the converse does not hold; some physical events are not mental events.
  2. The physical facts determine the mental facts (the supervenience thesis).
  3. Evolutionarily, the physical preceded the mental. Once upon a time, there were no minds; there was only matter. Now, there are minds; and their behavior is determined by the matter of which they are made. Mentality somehow evolved and arose out of the functioning of certain bits of matter (i.e., brains and nervous systems).

The physical aspects of our selves that are important for the "fixing" or "determining" of our mental lives are our brains and central nervous systems, along with the patterns of behavior in which we engage. The logical behaviorist (such as Ryle) stresses only the behavioral patterns (or dispositions), and does not inquire after neurological structure or functioning. The logical behaviorist is content to treat the mind/brain as a `black box' mediating between sensory stimuli and overt behavior. The structure and micro-functioning of the `wiring' inside the black box is seen as irrelevant for our possession of mental states. Or, if not irrelevant, then: inconsequential. For it possesses relevance only in so far as it creates and sustains the behavioral dispositions which themselves are definitive or constitutive of our occupying whatever mental states we do.

Once we move away from logical behaviorism, however, while remaining philosophical materialists, that internal structure and micro-functioning of the brain and central nervous system can assume new importance. For it can be incorporated into the supervenience basis of those physical facts that serve to fix or determine what the mental facts happen to be. The possibility now arises that mental states are enjoyed only by beings with a particular kind of `meatware' (brains); and that, no matter how similar in behavioral dispositions a differently constituted being (such as an android, or an alien silicone-based life form) might be, it cannot, metaphysically, have mental states because it is simply not made of the right kind of meat. This view might be called biological essentialism: it is essential, for mental life, to have a brain that is biologically broadly like ours. As John Searle puts it, it is only the brain that can secrete consciousness. No artificial gland could secrete the same.

In between the logical behaviorist, who does not care at all about the structure of the brain, and the biological essentialist, who might, arguably, care too much about it, is a third position: that of the functionalist. The functionalist cares about the structure of the brain only insofar as it needs to be able to harbor the various states in the program that, as far as the functionalist is concerned, constitutes the mind. The mind-as-program `runs on' the brain-as-hardware. Different hardwares can run the same program. Running a program is a matter of being able to make various transitions among `logical states' within the program. These transitions will be triggered by sensory inputs, and will produce behavioral outputs. Thus the functionalist is moved to say of mind that it's not the meat, but the logical motions that matter. (I owe this saying to Kim Sterelny.) The functionalist, unlike the biological essentialist, will think of a human being having the same kinds of mental states as an android or silicon-based alien, provided only that they all `function' the same way in producing like behavior in response to like sensory stimuli. If their programs are the same in each case, then so are their minds: for, according to the functionalist, the mind simply is the program.

Despite their differences on matters of detail, the logical behaviorist, the functionalist and the biological essentialist are all agreed on the more central materialist claim: that the mental supervenes on the physical. Their disagreements arise over exactly how such supervenience obtains.