Humean Dispositionalism

Humean metaphysics is characterised by a rejection of necessary connections between distinct existences. Dispositionalists claim that there are basic causal powers. The existence of such properties is widely held to be incompatible with the Humean rejection of necessary connections. In this paper I present a novel theory of causal powers that vindicates the dispositionalist claim that causal powers are basic, without embracing brute necessary connections. The key assumptions of the theory are that there are natural types of causal processes, and that manifestations of powers are identified with certain kinds of causal processes. From these assumptions, the modal features of powers are explained in terms of internal relations between powers themselves and the process-types in which powers are manifested. 1 Basic causal powers A number of philosophers claim there are properties which might be characterised as basic causal powers. In particular, those philosophers identifying themselves as “dispositional essentialists”, or simply “dispositionalists” appear to be committed to this idea.1 Causal powers have distinctive modal features. Frequently, such features are explicated by appeal to a necessary connection, perhaps between the instantiation of a power and the truth of a conditional sentence. If P is a power to yield response R to stimulus S, then whenever something x instantiates P, a conditional roughly of the form ‘If it were that Sx, then it would be that Rx’ will be true. Giving a precise account of the required conditional has proven difficult, but there is reasonably widespread agreement that the instantiation of a power necessitates the truth of a non-trivial modal proposition – typically a non-material conditional.2 1. Recent examples: Ellis 2001; Molnar 2003; Mumford 2004. This is a preprint of an article whose final and definitive form will be published in The Australasian Journal of Philosophy 2008; The Australasian Journal of Philosophy is available online at: http://journalsonline.tandf.co.uk/. The assertion that causal powers are “basic” is somewhat equivocal. It could suggest that the modal aspect of these properties is irreducible and primitive. It might also suggest, however, that the properties themselves are ontologically fundamental: that they might be among the elite, natural properties – those which carve nature at the joints. Obviously, neither of these interpretations excludes the other. No matter how the details are finally articulated, however, the existence of basic causal powers is widely thought to be incompatible with the Humean rejection of necessary connections between distinct existences. To demonstrate this incompatibility is difficult, given the lack of any widely agreed articulation. The general thought is that if some natural properties are essentially powers, or are essentially such as to confer certain powers, then it appears to follow that certain lawlike propositions about how the natural properties behave will be necessary truths.3 And if there are necessary laws or lawlike propositions, they clearly call for the very notion of necessary connection that a Humean takes herself to abjure.4 I take it, however, that the rejection of necessary laws is not an essential feature of the Humean view. Rather, the Humean is opposed to modal facts that are in some sense brute or primitive. The Humean is not, for instance, opposed to the idea that there could be a posteriori necessities, such as the identity of water and H2O. Necessities such as these, susceptible of explanation in terms of identity and rigid designation, are perfectly acceptable. It could turn out, then, that this is how laws are. Indeed, Alexander Bird [2001] has argued precisely this way with respect to the law that salt dissolves in water. Assuming that the fundamental laws are contingent, and using modally innocent claims about the meaning of “salt” and “water”, Bird has shown the plausibility of the view that such a law holds necessarily. For if we are to imagine a world where, in virtue of the fundamental laws being different, we would be tempted to assert that salt does not dissolve in water, then it is better to say that we are talking about a world without salt or a world without water. 2. Seminal papers on the analysis of dispositions in terms of modal conditionals include Bird 1998; Choi 2003; Gundersen 2002; Lewis 1997; Martin 1994. More recently, Michael Fara has suggested that conditionals are not appropriate for analysis of dispositions, but he does not thereby deny the modal nature of powers and dispositions [Fara 2005]. 3. E.g. Bird 2005; Ellis 2001: 52–3. Stephen Mumford [2004] suggests that the dispositionalist ought to be eliminativist about laws, but he still embraces necessary, lawlike truths, which appears to be enough for these purposes. 4. E.g. Lewis 1986b: 91.