To: Gordon F.
From: Geoffrey Klempner
Subject: Interactionist dualism versus epiphenomenal dualism
Date: 3 May 2007 12:10

Dear Gordon,

Thank you for your email of 28 April, with your essay for units 7-9 of the Philosophy of Mind program in response to the question, 'Contrast the main features of interactionist and epiphenomenalist versions of mind-body dualism,' and your response to my comments on your previous essay.

Interactionist and epiphenomenal dualism

One has to distinguish the notion of mind or soul in popular belief or, possibly, 'folk psychology' from the way these notions appear in the more sophisticated philosophical views represented by the interactionist and epiphenomenalist.

In popular belief, the mind or soul is 'contained' in the body. If materialism is true, and the mind is in some sense identical with a brain, then this belief turns out, literally, to be true. There might even be the possibility of taking the mind (brain) out of its container (body) and putting it in another container (a brain in a vat, or a brain, or rather, body transplant).

When Descartes sneers in Meditation 1 about the idea of the soul as a 'wind or vapour' he is thinking of the picture of literal containment. This is the sort of thing which spiritualists believe (hence photographs of 'ectoplasm'). Whereas in Cartesian dualism -- as in epiphenomenalism -- the mind/ soul is not conceived as itself located in space. The connection with body is purely through causation, either two-way, or one-way.

What is the specific difficulty with epiphenomenalism? why wasn't Descartes an epiphenomenalist?

You say that, 'it does look like an epiphenomenal point of view leads to difficulties that a container point of view doesn't. If only someone could find an object in a body which most everyone would agree is a mind!'

I'm not sure if you see the same difficulty with interactionism. But here's an argument for saying that the two theories are not the same in this respect.

Descartes believed that all non-human behaviour is physically caused, a sophisticated variety of clockwork (the technology of the day). If he had existed in the 20th century he might have embraced the AI view of non-human 'intelligence'.

If taking an angel's-eye standpoint one could somehow follow through all the causal connections in a non-human brain, there are no gaps, no unexpected events. Whereas human brains are different. Something weird goes on in the pineal gland. Impulses go in, and impulses come out, but nothing that occurs inside the pineal glad explains how the output is related to the input. That is because there is, in fact, a second input from the individual's non-physical soul.

In this sense, it is true that one can 'find' the interactionist's non-physical mind -- through the recognition that something is absent. Whereas with epiphenomenalism, the entire process proceeds in exactly the same way whether non-physical events are produced or not. Hence the zombie hypothesis. By hypothesis, my zombie double would write the very same words that I am writing to you now.

Contemporary dualists tend to be epiphenomenalists, since this is the only real possibility consistent with what we know about the way the brain works. Descartes wasn't in a position to know this, but would have rejected epiphenomenalism outright because it fails to defend the 'soul' of religious belief: not determined by physical causes, capable of surviving the death of the body and so on.

Further discussion of personal identity

Some philosophers have questioned the coherence of the idea of identity over time. So let's define 'GF' as an ordered series of momentary person stages connected by a suitably defined relation of spatio-temporal and psychological continuity.

When duplication occurs, the ordered series branches into two ordered series. Logically, we are free to describe the situation was one where two ordered series overlap, say, [a, b, c, d] and [a, b, e f], or as one where there one partially ordered set containing a, b, c, d, e and f.

I claim that this redescription adds nothing, nor does it take anything away from the original description in terms of identity over time. The criterion of spatio-temporal continuity under the covering sortal 'person', may be viewed as a 'criterion of identity over time', or merely as the rule for constructing the ordered set of person stages, if you do not accept the notion of identity over time.

Saying that there 'always were' two persons is mere logical stipulation. I don't see that this raises any problem of predestination. It seems odd that one can, by conducting a duplication, 'bring about' a state of affairs in the past. But, again, we are not really going against any basic understanding of causality. What is 'changed' in the past is not any actual events, but merely the way we describe those events in retrospect.

Psychological continuity is not the same as personal identity. In terms of the redescription as ordered series of person stages, there are ordered series which meet the conditions for psychological continuity but not for identity. The 'rule' of psychological continuity is less demanding than the one which is equivalent to a 'criterion of identity over time'.

Of course, this raises the question (as the Methuselah thought experiment is intended to do) whether any coherent account of a 'criterion of identity' can be given.

I am not seeking to establish that there are 'personal identities which are necessarily preserved over time' but merely that it is OK (contra Parfit) to believe in personal identity, to regard one's own personal identity as significant and not merely an illusion. Parfit sees the question as all-or-nothing. My preference is for a more pragmatic view.

All the best,

Geoffrey