Graduate Student, Philosophy
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Dr David Bain
Dr Stephan Leuenberger |
About
The short story
I am working on the problem of mental causation. In particular, I am examining the prospects for compatibilist responses to Jaegwon Kim's supervenience argument. I argue that if compatibilists are to stand any chance of success, then they must adopt an immanence model of the supervenience relation, examples of which include Yablo (1992), Shoemaker (2001), Pereboom (2002), and Bennett (2008). However, I also maintain, this kind of metaphysic comes with enough of its own difficulties that it can be concluded that Kim's argument has yet to be responded to satisfactorily.
The long story
From the perspective of commonsense, some claims just seem undeniably true. It seems undeniably true that throughout my life experiencing objects in front of me has caused me to believe that there are objects in front of me. It seems undeniably true that throughout my life the dull, empty pang of hunger has caused me to consume a large variety of foodstuffs. It seems undeniably true, indeed, that an enormously large number of experiences, sensations and other mental events continually cause any number of things, and that this seems to be the case for all people. The problem of mental causation is the problem of giving a satisfactory account of just how all of these seemingly undeniable claims are true; and it is a big problem because there is a consensus within the discipline that there is no consensus within the discipline that any of the large number of efforts to give such an account have been successful (Robb & Heil 2009). In fact, the various problems encountered by the various efforts have been so diverse and so deep that a few have concluded that at least some of those seemingly undeniable claims are false (Malebranche 1688/1997; Leibniz 1714/1898; Huxley 1874/2011; Robinson 1982; Jackson & Pettit 1990; Kim 2005; inter alios). Most are agreed, however, that such a conclusion is a philosophical refuge of last resort, a sentiment captured in Jerry Fodor’s famous remark that:
"If it is not literally true that my wanting is causally responsible for my reaching, and my itching is causally responsible for my scratching, and that my believing is causally responsible for saying… if none of that is literally true, then practically everything I believe about anything is false, and it’s the end of the world" (1990: 156).
This should not be seen as mere rhetoric. The problem of mental causation is one part of the mind-body problem, which is the problem of giving an account of the relationship between two things which seem prima facie distinct yet intimately connected: the mind and the body; or, as it is often put, the mental and the physical. One fundamental desideratum for such an account is that it ought to accommodate the truth of commonsense mental causation claims. The default view is that if one’s theory of the mind-body relation entails the falsity of such claims then so much the worse for one’s theory. Fodor’s remark neatly captures why: to deny mental causation claims would lead to such a massive revision of so many beliefs that are deeply embedded in our commonsense understanding of ourselves that there is an enormous burden of argument for any proponent of such revision to meet, and very strong reasons for developing theories which do not require it.
The force of this is worth spelling out. Consider just some of what appears to stand or fall along with mental causation: human agency, moral responsibility, knowledge and cognition. Voluntary action seems to require that beliefs, desires and intentions have appropriate causal inter-relationships, and are able to move muscle. Without voluntary action there is no human agency, and if no-one does anything voluntarily then it looks as if no-one can be morally responsible either. Also, if our perceptions, experiences and beliefs do not cause anything, then sensory learning, reasoning and memory would seem to be impossible – and all three are vital for human knowledge. Without agency and knowledge a massive part of cognition is already lost, but it gets worse. Even intentionality, the ability to think about things in the world, plausibly requires causal connections between mental events and events external to the thinker; and although a world in which there were mental effects but no mental causes might still be a world in which there was some intentionality, at best it would be of a very impoverished and isolated sort. Hence, if Fodor’s fear were to be realised and human agency, moral responsibility, knowledge, and cognition were to be revealed as mere fictions, then there is a very real sense in which it would be the end of the world.
This provides us with all of the materials required for a fundamental philosophical issue: the major challenge of accounting for a feature of the world that seems to many beyond doubt, and the apparent failure of the discipline to meet that challenge. This is a state of affairs which could lead to a negative conclusion regarding the possibility for a satisfactory account at all. But I believe that such pessimism, or mysterianism, would be misplaced, and not just because failure can often come very close to success, but because of the bounty of insights the various apparent failures have already produced.
That the problem is deep, but not bottomless, can be demonstrated by an examination of the mental causation debate, which I provide in my thesis by focussing on the most discussed, contemporary version of the problem, as encountered by a view of the mind-body relation called ‘non-reductive physicalism’. It is not a straightforward matter to say what non-reductive physicalism is, primarily because it is not a straightforward matter to say what reductionism and physicalism are. However, non-reductive physicalists at least hold that mental properties such as being an experience are not identical with physical properties such as being a brain state, rather mental properties merely supervene on physical properties in so far as there can be no change in the former without a change in the latter, and that mental properties depend on physical properties which are ontologically more fundamental and necessitate the mental properties which supervene on them. Thus the view is non-reductionist in that it at least denies mental-physical property identity. The view is physicalist in that it at least holds that everything is physical in a sense which at least respects the nothing over and above condition. There are various proposals for how to do this, but a popular one is to hold that to be physical is either to be directly mentioned in a completed physics, or to supervene on that which is directly mentioned in a completed physics. Crucially, the supervenience needs to be explained in a manner which rules out views such as emergentism which accept the supervenience claim but intuitively do not respect the nothing over and above condition. Non-reductive physicalism is probably the dominant view of the mind-body relation and, in one form or another, is held by, or has been said to be held by philosophers such as Hilary Putnam (1975), Ernest Lepore and Barry Loewer (1989), Jerry Fodor (1997), Lousie Antony and Joseph Levine (1997), Donald Davidson (2001), Derk Pereboom (2002), Karen Bennett (2008), and Christian List and Peter Menzies (2009).
According to Jaegwon Kim’s Supervenience Argument (1998; 2005; 2009), however, non-reductive physicalism entails the falsity of all commonsense mental causation claims. Kim derives this conclusion from the following principles which he contends either are, or should be accepted by non-reductive physicalists:
* Mental efficacy: there are mental causes that have systematic mental and physical effects.
* Physical causal closure: every physical effect has an immediate, sufficient physical cause.
* Mental-physical supervenience: mental properties strongly supervene on physical properties in that for any instantiated mental property M, necessarily there exists some physical property P such that the object instantiating M simultaneously instantiates P, and necessarily anything instantiating P at any time instantiates M at that time.
* Non-reducibility of the mental: mental properties are not identical with physical properties.
* Causal exclusion: it cannot systematically be the case that an effect has, simultaneously, two distinct immediate sufficient causes.
In brief, Kim employs these principles in the Supervenience Argument thus:
In order to bring about a mental effect: ME, the mental cause: MC, must bring about the physical effect: PE, which is the supervenience base of ME (argument stages 1-3).
But, because every physical effect has an immediate, sufficient physical cause, PE has an immediate, sufficient physical cause: PC (stage 4).
As PC is not identical to MC, PE has two distinct, sufficient causes: MC and PC. But PE cannot be overdetermined in this way, so one of its causes needs to be excluded with MC the clear candidate because of causal closure (stage 5).
Therefore, if non-reductive physicalism is true, there are no mental causes (conclusion).
On the basis of the Supervenience Argument, and the belief that there are mental causes, Kim then draws the further conclusion that non-reductive physicalism is false.
Given the inconsistency, at least one of the above principles must be false; and which is amended or abandoned determines one’s metaphysic of mind. If mental efficacy is denied then one is an epiphenomenalist. If causal closure is denied then one is an interactionist dualist. If non-reducibility is denied then one is a reductionist – this is the option Kim takes. Denying the exclusion principle is to be what is often called a ‘compatibilist’ (coined by Horgan 1997: 171), in so far as it is supposed to allow mental efficacy compatibly with physicalism and non-reduction. Compatibilism is by far the most popular response to Kim, and has been defended in one form or another by Terry Horgan (1997), Ausonio Marras (1998), Thomas Crisp and Ted Warfield (2001), Barry Loewer (2002), Eric Marcus (2005), Karen Bennett (2008), and Christian List and Peter Menzies (2009), inter alios.
However, I contend that without the following move of Stephen Yablo's, compatibilist responses are doomed to failure:
"There is a subtle interpretive question about supervenience. On the emergence interpretation, a thing's physical properties are metaphysically prior to its mental properties and bring them into being. To caricature emergentism just slightly, supervenience is a kind of 'supercausation' which improves on the original in that supercauses act immediately and metaphysically guarantee their supereffects... Another view is that the supervening mental properties are immanent in their physical bases; rather than giving rise to thought by some obscure metaphysical motion, certain material conditions are inherently conditions of thinking" (2008: 230n29).
Yablo maintains that with immanence there can be no causal competition between mental events and the physical events upon which they supervene any more than there can be causal competition between instances of red and instances of being red in a particular way, such as scarlet; also, with immanence there is still non-reduction. Although I agree that this, or similar solutions (e.g. Pereboom 2002; Shoemaker 2007; Bennett 2008), look like the best bet for non-reductive physicalists, I argue that much rests on what the immanence relation amounts to, and given the plausible conceptions of it a variety of problems emerge which look at least as troubling as those non-reductive physicalism was faced with in the first place.
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