The interaction problem, Part II

In an earlier post, I suggested that one of the advantages of hylemorphic dualism over Cartesian dualism is that its notion of formal causation allows it to sidestep the interaction problem. For if the soul is the form of the body, rather than a distinct substance in its own right, then there is no question of two substances having to “interact” in the order of efficient causes on the model of two billiard balls. There is rather just the one substance, a human being, having (as every other material substance has) two constituents, its form (or soul) and its matter (or body). The “interaction” between them is no more problematic than the “interaction” between the form of a tree and the matter that makes up the tree. For soul and body do not “interact” in the first place the way two distinct things do; they together constitute a single thing. My intention to raise my hand is not one event which has somehow to get into causal contact with another, physical event. It is rather the formal-cum-final cause of a single event of which the activity in my nervous system and arm is the efficient-cum-material cause. The solution to the “interaction problem” is to break out of the conceptual Procrustean bed of the mechanical picture of the world and return to a philosophy of nature informed by Aristotle’s four causes.

(Actually, saying that this “sidesteps” the interaction problem is misleading and anachronistic, since it conveys the false impression that hylemorphic dualism was motivated in part by a desire to solve the interaction problem. In fact there was no interaction problem until early modern philosophers like Descartes abandoned hylemorphism and redefined matter, mind, and causation in an explicitly anti-Aristotelian way. As I show in The Last Superstition, the “mind-body problem,” like the “traditional” philosophical problems of induction, personal identity, causation, and many others, is largely a consequence of the early moderns’ mechanistic revolution.)

Some modern dualists have suggested that the interaction problem is oversold in the first place. And they are right to complain that materialists fling it around much too glibly. To be sure, the interaction problem really is a problem for Cartesian dualism, but it is not (by itself, anyway) a refutation of it. Let’s briefly consider why – before going on to see why it is nevertheless a serious enough problem that any dualist is well-advised to consider opting for hylemorphic dualism over the Cartesian variety (especially given that, as I would argue, there is already ample independent reason to adopt hylemorphism as a general metaphysics).

One reason why the interaction problem does not strictly refute Cartesian dualism is that the Cartesian dualist could always simply deny that mind-body interaction is real in the first place, and opt for occasionalism, or parallelism, or epiphenomenalism. Of course, the extreme oddity of these views leads many critics of Cartesian dualism to regard recourse to them as little better than an admission of defeat, a desperate appeal to a deus ex machina. As Bill Vallicella notes (without necessarily endorsing the judgment) both Malebranche’s occasionalism and Leibniz’s pre-established harmony have been accused of deploying a deus ex machina strategy, especially since both literally appeal to God to resolve the question of the mind-body relationship.

But though the charge is common, it is unfair. Malebranche and Leibniz both had independent philosophical reasons for believing in God, and both also had independent reasons for denying that there could be causal interaction between created substances (any substances, not just mind and body). And given their respective specific understandings of the nature of substances, Malebranche had good reason to think that God continuously mediates between them, and Leibniz to think that God does not do so but instead established a universal harmony between them at creation. Hence, Malebranche quite naturally concluded that (for example) when you decide to have a beer your body moves towards the fridge, not because the decision causes the bodily movement, but because God, on noting that you have made that decision, causes the body so to move. And given his different conception of substance, Leibniz quite naturally concluded instead that the decision and the bodily movement in question were each simply the natural unfolding of what was pre-programmed into each substance at their creation. These views of the mind-body relationship were not developed simply to deal with the interaction problem, but flowed naturally from two sophisticated and independently defensible metaphysical positions.

Defensible, but still bizarre, rarely actually defended, and subject to various objections of their own. And most modern dualists would agree with materialists that it would be preferable to avoid occasionalism and pre-established harmony if one can manage it. Hence the greater popularity of epiphenomenalism, according to which mental events do not cause physical events but are rather merely the ineffectual byproduct of the flux of physical events. When you decide to have a beer, the decision itself (or at least the conscious awareness of it) is not what causes your body to walk over to the fridge. Rather, entirely unconscious physical events caused your body to do so, and in the process also caused the conscious experience of making the decision in question, which event itself had no causal efficacy at all.

Though not much less bizarre than occasionalism and pre-established harmony, epiphenomenalism at least has this advantage over them as a way for Cartesian dualists to deal with the mind-body problem: Materialists too seem led into it, so that they can’t plausibly use it as a stick with which to beat dualists. For materialist theories of mind have a notorious problem explaining the efficacy of mental content. If (as materialists tend to hold) it is only the physical properties of mental states which give them their power to cause other physical states, then their mental or intentional content seems epiphenomenal. For example, if we suppose, as a materialist might, that my decision to have a beer is identical with or at least supervenes upon some event in my nervous system, then if it is only the physiological properties of that event that enter into the explanation of how it caused my bodily movements, the fact that it involved a representation of beer, specifically, or indeed had any representational content at all, drops out as causally irrelevant.

So, if materialists as well as Cartesian dualists are faced with the possibility of having to swallow epiphenomenalism, the former cannot accuse the latter of having a special difficulty in accounting for mind-body interaction. Still, this is more a rhetorical victory for Cartesian dualism rather than a substantive one. For epiphenomenalism is notoriously unsatisfactory, and not just because it is odd to say that your decision to have a beer is not what caused you to go to the fridge. If our mental states can have no causal influence whatsoever on our bodies, it would seem to follow that we cannot even talk about them. Indeed, the epiphenomenalist himself could not even talk about his thoughts about epiphenomenalism. For those thoughts would be as inefficacious as any other mental state or event. When he says “Epiphenomenalism is true,” the fact that he thinks it is true has absolutely nothing to do with his saying so. This is bizarre at best and incoherent at worst. And though epiphenomenalists have tried to find various ways around the problem, it would be better not to have to deal with it in the first place.

So, a Cartesian dualist is well-advised not to deny that mind and body interact. And this brings us to the second reason why a Cartesian dualist has a right to complain that his critics’ appeal to the interaction problem is often too glib. As Bill Vallicella has pointed out in several past posts, whether a Cartesian dualist can account for mind-body interaction depends on what view of causation one is assuming. And there is at least one view of causation – a regularity theory – on which no interaction problem arises at all for Cartesian dualism. As Bill has suggested:

Suppose we say that:

Event-token e1 causes event-token e2 if and only if (i) e1 temporally precedes e2, and (ii) e1 and e2 are tokens of event-types E1 and E2 respectively such that every tokening of E1 is followed by a tokening of E2.

On this Hume-inspired theory (sans the contiguity condition), causation is just regular succession. If this is the correct theory of causation, then there is nothing problematic about mental events causing physical events, and vice versa.

About this, Bill is absolutely right. If such a regularity analysis is correct – and there are philosophers who would defend such an analysis on grounds independent of their position on the mind-body problem – then the interaction problem is solved. At the very least Cartesian dualists can plausibly hold that objections to their position based on the interaction problem are less conclusive than their critics often let on.

But the “if” in question is a very big one. Is such a regularity theory of causation really plausible in the first place, or at least plausible enough to show that Cartesian dualism really can account for mind-body interaction after all? I think not. One reason why is that apart from its use of the word “cause,” the proposed analysis is perfectly compatible in substance with occasionalism, parallelism, and epiphenomenalism. For on each of those views, it is perfectly possible to say that a mental event of type M is always followed by a physical event of type P, in which case, on Bill’s suggested regularity theory, M will count as the cause of P. But an “interactionist” theory which differs in substance not at all from occasionalism, parallelism, or epiphenomenalism – all of which deny interaction – is an “interactionist” theory in name only.

Another problem with the proposed regularity analysis is that it simply doesn’t capture what we mean by “cause.” As Hume himself recognized, the connection we take to hold between a cause and its effect is not just a regular one, but also a necessary one. We don’t just think A was in fact followed by B, but that in some sense it had to be followed by B. Of course, Hume thinks there is no objective source for this idea of necessity, that it has to be traced to a purely subjective expectation on our part. For he holds that there is nothing in our ideas either of a cause or of its effect that necessarily links them together. Objectively speaking, causes and effects are “loose and separate,” and any effect or none could in theory follow upon any cause.

This Humean result is what makes “regularity” theories of causation seem at all plausible. But what they really give us is not causation, but rather only some replacement for causation. (The same holds true, I would say, for counterfactual analyses of causation.) So, no appeal to such a theory really solves the interaction problem at all. Rather, it simply adds one mystery to another, saying, in effect: “Causation in general is already mysterious, so why shouldn’t mind-body interaction be?”

The thing is, the reason causation in general is mysterious is the same reason mind-body interaction in particular is: the mechanistic revolution that displaced the Aristotelian-Scholastic model of explanation, throwing out formal and final causes and trying to make do with bastardized versions of material and efficient causes. As I have noted in earlier posts and discuss at length in TLS, one of the main arguments the Aristotelian tradition gives for formal and final causes is that without them efficient causation becomes unintelligible. Unless there is something in the nature (or “substantial form”) of a thing by virtue of which it “points to” or is “directed at” the generation of a certain effect (as its final cause) then there is no way to account for why exactly it produces that effect as opposed to some radically different effect, or none at all. Hume was merely drawing out the inevitable consequences of the mechanistic revolution. (And even here Hume is, as always, overrated, since the skepticism vis-à-vis causation implicit in the rejection of formal and final causes was already foreshadowed in Ockham and the late medieval nominalist tradition.) The way to solve both the interaction problem and the problem of causation is, accordingly, the same: a return to the Aristotelian metaphysics early modern philosophy displaced.