Powers and Downward Causation
One of the main problems for non-reductive physicalism, 1 according to which mental properties are distinct from and not reducible to the physical properties which underlie them, is widely taken to be the so-called problem of downward causation. This problem, which has been developed, in particular, by Jaegwon Kim in a series of papers since the 1980s,2 is meant to present a general obstacle to the possibility that macroproperties, such as mental properties, could be distinct from underlying microproperties, but still depend on the latter’s instantiation, while playing a genuine causal role of their own. As Kim argued for the case of mental phenomena, such a causal role would have to involve a ‘downward’ causal influence onto the level of physical and microphysical phenomena, which would conflict with some key tenets of naturalism. Kim thought that this problem would proliferate to exclude any causal influence of mental phenomena and make them generally epiphenomenal, unless they could be identified with physical phenomena. Since such epiphenomalism about mental properties is an extremely unattractive option, this result would severely undermine the project of non-reductive physicalism as a whole.
In this paper, I want to examine to what extent the force of Kim’s challenge is affected by the increasing shift from a ‘Humean’ metaphysical framework towards a neo-Aristotelian ‘power ontology’, which has been taking place in metaphysics during the last twenty years. For while Kim’s argument has been the object of intense discussion, it is noticeable that most of this debate has been conducted within a broadly ‘Humean’ metaphysical framework. (Even though a ‘causal powers’ terminology has sometimes been used to set up the problem.) This metaphysical framework is—for the purposes that interest me here—characterised by three interrelated key features.
First, it is a framework which rejects the idea of powers as genuine properties on a par with non-power (categorical) properties. Instead, it accepts only the latter kinds of properties as bona fide and fundamental properties, and to the extent that powers are accepted at all, their possession is taken to be reducible to the possession (and causal influence) of such other properties. (While Kim occasionally uses the phrase ‘causal powers’ himself, it is quite clear that by this he does not mean anything like Aristotelian powers, but rather uses “X’s causal powers” as shorthand for “what X can cause”).3 Second, this framework includes only events, which are considered as separate and ‘atomic’, among its ontology of changes. It does not include processes which have intrinsically connected stages (i.e. stages whose nature and identity depend on the process of which they form a part). And third, it is a framework which takes event-causation—rather than substance-causation or causation by properties—to be the only acceptable form of causation.
In the last twenty years, much of this framework has come under increasing pressure, and it no longer holds sway as the undisputed majority view. Instead, many philosophers are nowadays willing to countenance the idea that there are powers which are both real and bona fide properties of substances and whose possession and exercise are not reducible to the possession of non-power properties and to the latter’s causal influence. I will argue that this shift towards a Neo-Aristotelian realism about powers should also change our assessment of Kim’s downward causation argument. For, as I will try to show, realists about powers face a challenge which has interesting similarities to Kim’s own downward causation argument. For there is a structurally similar argument to the effect that powers cannot make any genuine causal contribution because all steps in the processes which occur when powers are manifested, as well as the end-states of these processes, are already causally explained by other features. But, qua realist about powers, one will have to reject this result; and one can best do so, I will suggest, by denying the argument’s underlying assumption that powers must ‘compete’ with certain other features for causal influence. This response will also undermine the force of Kim’s original downward causation objection, insofar as higher-level powers are concerned, since Kim’s argument, too, crucially rests on a ‘competition for causal influence’ assumption (regarding the relation between higher-level and lower-level phenomena).4
I will, first, briefly sketch the view of powers I will be presupposing here (sec. 2) and rehearse the version of Kim’s argument I will be concerned with (sec. 3). I will then set up the structurally similar argument against the causal relevance of powers (sec. 4), before turning to the question of how we can meet this argument and how our answer will impact on Kim’s own downward causation argument (sec. 5).