Glossary and Notational Conventions
For the purposes of this handout, lower-case letters will name particular events (i.e. event tokens). Capital letters will represent properties or event types. So m might be a particular mental event (say, my having a headache at a particular time), and M might be a general type of mental event (say, having a headache).
Nomological. Involving laws (from nomos, which means law). So e.g. "the nomological conception of causality" is the idea that, if one event causes another, then there is a universal law that events of the same type as the first always lead to events of the same type as the second. Similarly, the "anomalism of the mental" means that the mental is not lawlike, that is, that there are no exceptionless laws involving mental types.
Determinate/determinable. A determinable property is a property like being red or walking, where there are many different more specific ways of having the property. Something can be red by being crimson, or scarlet, or . . .. Someone can walk by walking rapidly, walking slowly, shuffling, etc. (Recall the old "walk this way" joke.) So crimson and scarlet are determinates of the determinable red; walking rapidly and shuffling are determinates of the determinable walking.
Dualism and Mental Causation
Mental causation has always posed a problem for dualism. (As Kim discusses in Chapter 2, Princess Elizabeth of Bohemia corresponded with Descartes about the issue.) It has always seemed mysterious how something nonphysical could possibly have causal effects on something physical. Kim suggests that some versions of materialism (in particular, the "nonreductive physicalism" defended by Fodor, which seems to be very close to functionalism) may also face problems about how mental causation is possible.
Let's start by seeing how physicalism at first seems to solve dualism's problem with mental causation.
Consider a token mental event m (my intention to raise my arm at a particular time) which causes a physical event p (my arm going up). So we have:
m --> p
On the other hand, if we believe in the causal closure of the physical, then we will also think that there was a complete physical cause c of p. But now the idea that m caused p seems superfluous: if p has a complete physical cause, what's the role of m in bringing it about? p does not seem to be overdetermined: that is, it does not seem that p has distinct causes either of which would have brought it about in the absence of the other. If that's right, then we cannot say that m and c are distinct causes of p. So it looks like we have:
m
c --> p
Physicalism seems to resolve this problem. According to physicalism, m = c. The mental event is identical with a physical event, so there is no danger that the existence of a physical cause will "exclude" the mental cause. Instead, the physical cause just is the mental cause!
Kim: Three Problems of Mental Causation
Kim surveys three problems related to mental causation, but only discusses one in depth (namely the third, the "problem of causal exclusion").
1. The problem of anomalous mental properties.
1. There are no exceptionless laws involving psychological notions. (The "anomalism of the mental.")
2. If event e1 causes event e2, then there must be an exceptionless law connecting events of the same type as e1 with events of the same type as e2. (The "nomological conception of causation.")
3. If e1 causes e2 because e1 is of mental type M, then the law connecting e1 and e2 must involve events of type M. (That is, the "events of the same type as e1" mentioned in premise 2 must be events of type M.)
Therefore,
4. Mental events do not cause physical events because of the kind of mental event they are.Davidson argues for premise 1 by pointing out that there seems to be a kind of incommensurability between the way we ascribe mental properties and the way we ascribe physical ones. Mental ascription depends on a holistic rationality constraint, while physical ascription doesn't. This makes it hard to see how the two could match up in the way required by strict psychophysical laws.
Note that even if this argument is sound, it does not follow that mental events don't cause physical events at all. The same event will fall under many types. In particular, a mental event m may fall under both a mental type M and also a physical type P. (For example, perhaps m is a particular headache; M is the property of having a headache; and P is the property of having one's C fibers firing. The particular headache m could be an instance of both M and P. And even if there are no laws involving M, there may be laws involving P.)
In fact, Davidson regarded these considerations as providing an argument for the view that all mental events are also physical events (i.e. for token physicalism, though not for type physicalism). If mental events cause physical effects, and if this requires general laws, but the general laws cannot involve mental types, then the general laws can only involve physical types, implying that all mental events are also physical!
The most likely points at which to attack the argument are premises 1 and 2.
One might try to argue that strict psychophysical laws are possible, contrary to premise 1.
Or one might try to argue that causation does not require general laws linking types of events. The main rival view of causation is the counterfactual analysis, due to David Lewis. Kim argues that the counterfactual analysis does not escape the need for general laws. (Either laws re-enter the picture directly in the analysis of what it is for a counterfactual to be true, or else they enter indirectly in the analysis of what it is for possible worlds to be similar.)
2. The problem of causal exclusion.
Kim argues that functionalism and, more generally, "nonreductive physicalism," faces a serious problem in accounting for mental causation.
Consider a case in which a mental event m of mental type M causes a physical event p. (Recall that lower-case letters represent events, upper-case letters represent types or properties.)
1. p has a complete physical cause c. (causal closure of the physical)
2. c causes its effect by virtue of its physical type C.
3. Even if m = c, M ≠ C. (This follows from nonreductionist physicalism, e.g. functionalism. For an identity theorist, of course, M = C.)
Therefore,
m does not cause p by virtue of its mental type M.Kim presses this argument further on pp. 198-200 by arguing that if mind-body supervenience holds, then the causal exclusion argument can be extended to show the impossibility, not only of mental-to-physical causation, but also of mental-to-mental causation.
One interesting response to the causal exclusion problem can be found in Stephen Yablo, "Mental Causation," Philosophical Review 101 (1992): 245-280. I summarize it in a different version of this handout: see the last section of http://www.trinity.edu/cbrown/mind/mentalCausation.html.
3. The problem of intrinsic mental properties.
1. The semantic properties of mental states (i.e. what they are about) are not intrinsic. (They depend on facts about the individual's history and environment.)
2. What an event causes depends only on the current, intrinsic properties of the event.
Therefore,
3. Mental events do not cause other events by virtue of their semantic properties. (So, for instance, the content of my beliefs does not play a role in determining what they cause.)The issues here are addressed in more detail in Kim's Chapter 9.