Anomalism and Supervenience: A Critical Survey

I Introduction

The thesis that mental properties are dependent, or supervenient, on physical properties, but this dependence is not lawlike, has been influential in contemporary philosophy of mind. It is put forward explicitly in Donald Davidson's seminal 'Mental Events.' On the one hand, Davidson claims that the mental is anomalous, that 'there are no strict deterministic laws on the basis of which mental events can be predicted and explained' (1970, 208), and, in particular, that there are no strict psychophysical laws. On the other hand, he insists that the mental supervenes on the physical; that 'mental characteristics are in some sense dependent, or supervenient, on physical characteristics' (1970, 214).

Though the thesis has its appeal, some find it untenable. Jaegwon Kim, for example, argues that psychophysical supervenience inherently entails psychophysical laws - 'if you want psychophysical dependence, you had better be prepared for psychophysical laws' (1984, 171) - and hence is at odds with mental anomalism. The paper has three objectives, the first of which is to show that Kim's argument is very general and applies to a wide variety of notions of supervenience, including the different notions of global supervenience found in the literature (section III). A second goal is to evaluate several more recent attempts to defend the compatibility of supervenience and anomalism. I focus on four Davidsonian responses to Kim's argument (sections IV-VII); three were offered by Davidson himself, and one by William Child. I argue that the responses do not fully address Kim's challenge, and that they can succeed only if we relinquish other central theses of Davidson's philosophy. The last objective is to outline a different Davidsonian response to Kim's challenge (section VIII).

II Indiscernibility, dependence and irreducibility

Let us start with some preliminaries concerning the relations between supervenience, dependence, and psychophysical laws. Supervenience has an interesting history that goes back to Leibniz.¹ Davidson, who is the first to apply it in the psychophysical context, borrows the notion from Moore and Hare, who introduce it in the context of ethics.² In a landmark passage in 'Mental Events,' Davidson writes:

Although the position I describe denies there are psychophysical laws, it is consistent with the view that mental characteristics are in some sense dependent, or supervenient, on physical characteristics. Such supervenience might be taken to mean that there cannot be two events alike in all physical respects but differing in some mental respect, or that an object cannot alter in some mental respects without altering in some physical respects. Dependence or supervenience does not entail reducibility through laws or definition…

(1970, 214)

The passage draws attention to three important questions relating to supervenience: how it is characterized, how it is related to dependence, and how it is related to irreducibility.³ Let me consider them in turn. First, the characterization of supervenience. Davidson starts with a characterization in terms of indiscernibility, namely, that 'there cannot be two events alike in all physical respects but differing in some mental respect,' that is, there cannot be two events that are physically indiscernible but mentally discernible. He then offers another characterization of supervenience, one that construes it as a type of covariance: 'an object cannot alter in some mental respects without altering in some physical respects,' that is, mental changes co-vary with physical changes.

In his more recent writings, Davidson provides additional covariance definitions, the gist of which is that any mental difference between objects must be accompanied by a physical difference. In 'Reply to Harry Lewis,' Davidson writes:

The notion of supervenience, as I have used it, is best thought of as a relation between a predicate and a set of predicates in a language: a predicate p is supervenient on a set of predicates S if for every pair of objects such that p is true of one and not of the other there is a predicate in S that is true of one and not of the other.

(1985, 242)

And in his 'Thinking Causes,' he makes a similar claim:

[T]he idea I had in mind is, I think, most economically expressed...