Interventionism and Epiphenomenalism

I Introduction

One of the central objectives Shapiro and Sober pursue in (2007) is to show that what they call the master argument for epiphenomenalism, which is a type of causal exclusion argument, fails. Epiphenomenalism, according to the terminology adopted in (Shapiro and Sober 2007), designates the thesis that supervening macro properties (or variables or factors) have no causal influence on micro properties that are caused by the micro supervenience bases of those macro properties. Well-known classical exclusion arguments are designed to yield such macro-to-micro epiphenomenalism along the lines of the following reasoning: subject to the widely accepted principle of the causal closure of the physical, there exists a causally sufficient micro cause for every micro effect; if it is additionally assumed that macro properties supervene on micro properties without being identical (or reducible) to the latter and if—in light of the rareness of cases of causal overdetermination—micro effects are assumed not to be systematically overdetermined, it follows that macro properties are causally inert with respect to effects of their micro supervenience bases.² This result directly contradicts one of the principal tenets of non-reductive physicalists who, in a nutshell, subscribe both to the causal closure of the physical and to the non-reductive supervenience of macro on micro properties, yet nonetheless insist on the possibility of downward causal dependencies as are e.g. involved in mental-to-physical or biological-to-physical causation.

Shapiro and Sober (2007) reject the traditional line of reasoning against non-reductive physicalism by claiming that an interventionist theory of causation, as most exhaustively developed in (Woodward 2003), which has gained wide acceptance and popularity in recent years does not rule out causal dependencies among supervening macro properties and effects of their supervenience bases. In consequence, they argue that if the master argument for epiphenomenalism is based on an interventionist notion of causation it is rendered invalid. Shapiro and Sober (2007) not only hold that (i) interventionism blocks the epiphenomenalist's master argument and, thus, immunizes non-reductive physicalism against exclusion arguments by paving the way for a causal interpretation of downward dependencies, they moreover maintain that (ii) the interventionist framework provides a methodology or tool to identify the micro effects of macro properties.³

In this paper, I intend to challenge both of the claims (i) and (ii). It shall be shown that spelling out causation in interventionist terms in no way blocks the master argument, but, rather, gives rise to a self-contained interventionist master argument for epiphenomenalism which, very broadly, involves the following three premises: (I) Woodward's interventionist theory of causation, (II) the assumption that macro properties supervene on micro properties without being identical to the latter, and (III) the assumption that the micro supervenience bases of macro properties are causally connected to the arguable micro effects of those macro properties. These premises—contrary to Shapiro's and Sober's assessment—shall be demonstrated to imply that macro properties are causally irrelevant to effects of their supervenience bases. In sum, thus, the first part of this paper aims to substantiate that, rather than supporting non-reductive physicalism, Woodward's interventionism is incompatible with non-reductive physicalism. The second part then discusses two conceivable modifications of Woodward's theory that both ensure the compatibility of interventionism and non-reductive physicalism. Nonetheless, neither of these modifications shall turn out to suit the purposes of non-reductive physicalists, for neither of them allows for establishing the actual existence of macro-to-micro causation nor for testing the downward causal powers of supervening properties.

Endorsing the epiphenomenalist conclusion of the master argument is, despite the latter's validity, not my aim here. I agree with Shapiro and Sober as regards the falsity of the conclusion of the master argument. What is more, macro-to-micro causation cannot actually be ruled out as impossible on the mere basis of (I) to (III). Whether there exists macro-to-micro causation is a matter that is to be settled by scientific investigation and not by some a priori philosophical argument (cf. Shapiro and Sober 2007, 259). Accordingly, I take...