Interactionist substance dualism in the philosophy of mind is supposed to face a devastating objection, the interaction objection. In the first part of this post I will present this objection in its traditional form and suggest that it is not all that serious. In the second part, however, I take the objection seriously and consider whether Aristotelian- Thomistic hylomorphism has the resources to counter it.
I. The Traditional Interaction Objection
It is a given that mind affects body, and body mind. Suddenly remembering the bottle of single-malt Scotch that Harry gave me for my birthday, I am inspired to get out of my chair and pour myself some. After consuming a generous portion, I note that my mental state has altered appreciably. The mental event of remembering causes the physical event of drinking which in turn elicits the mental state of elation, which may bring in its train some loss of motor control. But how are such interactions possible if mind and body/brain are distinct types of substance, one spatial the other nonspatial? As Elliot Sober put it recently:
If the mind is immaterial, then it does not take up space. But if it lacks spatial location, how can it be causally connected to the body? When two events are causally connected, we normally expect there to be a physical signal that passes from one to the other. How can a physical signal emerge from or lead to the mind if the mind is no place at all? (Philosophy of Biology ,Westview 2000, 2nd ed., p. 24)
The above is a piece of philosophical boilerplate endlessly repeated in the materialist literature. I confess to a difficulty in seeing just what this objection is supposed to be. If Sober is saying that all causation must involve physical contact between cause and effect, then he simply begs the question against the dualist. He simply asserts something that the dualist denies. Is it obvious what the correct theory of causation is? Is it obvious that all causation involves physical contact between cause and effect and the transfer of some physical magnitude from cause to effect? Certainly not inasmuch as there are a number of competing theories of causation, among them counterfactual theories, transfer theories, and nomological theories, to name just three broad types. Given that the nature of causation is up for grabs, and given that the interaction objections requires a transfer theory of causation, one should conclude that the interaction objections is the exact opposite of decisive.
If interactionist dualism is true, then there are cases of causation that do not operate by physical contact. One cannot refute this by saying, or implying, that all cases of causation operate by physical contact. At this point I will be told that dualist interaction is unintelligible. But why? If you say that it is because dualist interaction does not fit the physical-physical pattern, then again you beg the question. If you say that every case of causation involves an intervening mechanism, but there isn't one in the dualist case, then you beg the question in a slightly more subtle way. For what the dualist holds is that there are cases of direct causation. It is not clear that all physical-physical causation is indirect, but even if it were, this putative fact is not a reason to think that all cases of causation are indirect.
But how does mental-physical causation work? If this is a demand for a specification of the intervening mechanism, then the question rests on a false presupposition, namely, that there must be such a mechanism. If, on the other hand, the demand is for a specification of the causally relevant properties and covering laws, then I see no reason why this demand cannot be met.
I think that there is less to the traditional objection than meets the eye: it gives the interactionist dualist little reason to abandon his view.
II. A Hylomorphic Solution
But perhaps I'm wrong — in the good company of Curt Ducasse, John Foster and a few others. Legions of philosophers have taken the objection sketched above to be crushingly strong. A drastic way of meeting it is by retaining a dualism of substances while denying interaction. Occasionalists, parallelists, and epiphenomenalists deny interaction. But I mention them only to set them aside. An alternative is to hold to interaction while denying dualism. Here we meet materialists and idealists. But brevity is the soul of blog, so I set them aside as well. This brings us to what might be called hylomorphic dualist interactionism. Is it superior to substance dualist interactionism? That is the question.
For the hylomorphist, every material substance is a compound of form and matter. Human beings are no exception. In them, anima forma corporis: the soul is the (substantial) form of the body. Soul is to body as form to matter. The form and matter of a material substance are not themselves (primary) substances: they are not capable of independent existence. They are rather 'principles' uncovered in the analysis of material substances. This is a key difference between substance dualism and hylomorphic dualism. If the mind is a (primary) substance, then it can exist on its own, where 'can' expresses broadly logical possibility. But if the mind or soul is the substantial form of the body, then it cannot exist on its own. It needs matter both to exist and to be individuated.
Thus the hylomorphic dualist, while remaining a dualist, makes a significant concession to materialism. Human minds are essentially embodied minds. Before my conception, there was no res cogitans 'with my name on it,' so to speak. I did not pre-exist my conception. I came into existence at conception. (That I am wholly dissolved in death is not admitted by Thomists, inasmuch as they hold that the human soul is a subsistent form; but let us not worry about this special problem now.) Human minds are essentially enmattered minds in at least this sense: no human mind can exist without at some time being embodied. According to Edward Feser, a consequence of the hylomorphic view is that:
. . . there is no mystery about how soul and body get into causal contact with one another, for the soul-body relationship is just one instance of a more general relationship existing everywhere in the natural world, namely, the relation between forms . . . and the matter they organize. If this general relationship is not particularly mysterious, neither is the specific case of the relationship between soul and body. The mistake of Cartesian dualists and materialists alike, according to the hylomorphist, is to think of all causation as efficient causation. When it is allowed that there are other irreducible modes of explanation — in particular, explanation in terms of formal causation — the interaction problem disappears. (Philosophy of Mind: A Short Introduction, p. 176)
Feser here makes two main points. The first is the the soul-body relation is a special case of the form-matter relation; as such, the former is no more problematic than the latter. The second point is that the relation between soul and body is one of formal, not efficient, causation. The two points are logically connected: if the soul is the form of the body, and if the two are causally related, then it is difficult to see how the relation could be one of efficient causation. An efficient cause is either an agent-cause or an event-cause. But forms are neither agents nor events.
Hylomorphism undoubtedly reduces the 'ontological distance' between mind and body, a 'distance' that is troubling on substance-dualist conceptions, but I honestly do not see how hylomorphism solves the problem of interaction. We are assuming that there is interaction, two-way causal influence. We are also assuming dualism in a sense stronger than mere property-dualism: 'hylomorphism' is not just a name for a version of supervenience physicalism. Now interaction is, by definition, efficient-causal interaction. Mental events bring about physical events and physical events bring about mental events. To interpret this interaction in terms of formal causation seems tantamount to denying that there is any interaction. Iteraction is efficient-causal interaction. Formal causation appears irrelevant to it.
To revert to my example, my sudden remembering of having been given a bottle of Scotch is an event-token that enters into the etiology of my rising from my chair. It is rather unclear how this event could be the form of anything in the body. For one thing, the event of remembering is temporally prior to any of the events involved in my rising from my chair. Forms, however, are not temporally prior or posterior to what they inform. So it seems clear that a mental event cannot stand to a physical event it causes in the relation of form to matter.
Turning now to the contemporary Thomist John Peterson for instruction, we read:
. . . it is just because Peter's human essence or form is in matter that Peter's intellect and will are not to be confused with the intellect and will of a pure spirit. But if this confusion is not made, then the question of how Peter's supposedly purely spiritual volitions can cause the movements of his arms and legs does not even arise. ("Persons and the Problem of Interaction," The Modern Schoolman, January 1985, p. 136)
I fail to see how this does anything to solve the problem of interaction under the two conditions specified above, namely, that there is interaction, and that mind is irreducible to body. We are told that Peter's human essence is in matter. Fine, he is not a disembodied spirit. But that which thinks in me, if a res cogitans, is also not a disembodied spirit. So merely pointing out that a mind is not disembodied does nothing to solve the interaction problem. And saying that the mind is the form of the body also does nothing to solve the problem. For as I said above, the problem of interaction is a problem of efficient causation, not one of formal causation as alone would be be appropriate if the mind were the form of the body.
Whatever merits hylomorphism may have, it seem quite irrelevant to the interaction problem.