The interaction problem

Aristotle and the Scholastic tradition influenced by him famously held that to understand a thing required knowing each of its four causes: its material cause, the stuff out of which it is made; its formal cause, the specific form or essence that stuff has taken on, and which makes it the kind of thing it is; its efficient cause, that which brought it into existence; and its final cause, the end or purpose toward which it is directed. Modern thought is largely defined by its rejection of two of Aristotle's four causes. For the moderns, there are no such things as substantial forms or fixed essences, and there are no ends or purposes in nature. There are just brute material elements related by purposeless, meaningless, mechanical chains of cause and effect.

As I have emphasized in my series of posts on dualism, this “mechanical” conception of nature, insofar as it stripped matter of anything smacking of either goal-directedness or sensible qualities as common sense understands them, and relocated these features into the mind, more or less automatically entailed a Cartesian form of dualism on which intentionality and qualia are immaterial as a matter of conceptual necessity. But it also automatically entailed that this form of dualism would suffer from the notorious “interaction problem.”

For the moderns, all causation gets reduced to what the Aristotelians called efficient causation; that is to say, for A to have a causal influence on B is for A either to bring B into being or at least in some way to bring into existence some modification of B. Final causality is ruled out; hence there is no place in modern thought for the idea that B might play an explanatory role relative to A insofar as generating B is the end or goal toward which A is directed. Formal causality is also ruled out; there is no question for the moderns of a material object’s being (partially) explained by reference to the substantial form it instantiates. We are supposed instead to make reference only to patterns of efficient causal relations holding between basic material elements (atoms, or corpuscles, or quarks, or whatever).

Thus, if the mind considered as immaterial is to have any explanatory role with respect to bodily behavior, this can only be by way of some pattern of efficient causal relations – to put it crudely, in terms of a Cartesian immaterial substance (or perhaps various immaterial properties) “banging” into the material substance (or material properties) of the brain like the proverbial billiard ball. How exactly this is supposed to work is notoriously difficult to explain. We’ve got two independently existing objects (or two independently existing sets of properties) somehow interacting the way physical particles or billiard balls do, or perhaps the way waves or fields of force do – except that one of these objects (or sets of properties) is utterly devoid of any of the material features that make it possible for something to count as a particle, billiard ball, wave, or field of force. Add to this considerations like the conservation of energy and interaction between the material and immaterial realms comes to seem ruled out in principle by our current understanding of the way the material world works.

But from an Aristotelian-Scholastic point of view, this whole picture of the mind-body relationship is hopelessly wrongheaded from start to finish. It is wrong to think of the soul (of which the intellect is for Aristotelians but a part, not the whole) and the body as independent objects in the first place. The soul is rather a form that informs the matter of the body and the body is the matter which is informed. As with the form and matter of a stone, tree, or earthworm, what we have here are not two substances interacting via efficient causation, but rather two metaphysical components of one substance related by formal causation. As the form of the stone is to the matter making up the stone, the form of the tree to the matter making up the tree, and the form of the earthworm to the matter that makes up the earthworm, so too is the human soul to the human body. There is in principle no such thing as the matter of a stone, tree, or earthworm apart from the form of a stone, tree, or earthworm respectively, and no such thing as the form of any of these things existing apart from their matter. The form and matter don’t “interact” as if they were two distinct objects; rather, the form constitutes the matter as the (one) kind of object it is in the first place.

Similarly, there is in principle no such thing as the matter of a living human body without a human soul and there is in principle no such thing as a human soul which is not the soul of some body. (This does not entail that the soul cannot survive the death of the body, only that it could not have existed in the first place unless it was united to some body; but this is a topic that can be bracketed off for present purposes.) The soul doesn’t “interact” with the body considered as an independently existing object, but rather constitutes the matter of the human body as a human body in the first place, as its formal (as opposed to efficient) cause.

As I move my fingers across the keyboard, then, what is occurring is not the transfer of energy (or whatever) from some Cartesian immaterial substance to a material one (my brain), which sets up a series of neural events that are from that point on “on their own” as it were, with no further action required of the soul. There is just one substance, namely me, though a substance the understanding of which requires taking note of each of its formal-, material-, final- and efficient-causal aspects. To be sure, my action counts as writing a blog post rather than (say) undergoing a muscular spasm in part because of the specific pattern of neural events, muscular contractions, and so forth underlying it. But only in part. Yet that does not mean that there is an entirely separate set of events occurring in a separate substance that somehow influences, from outside as it were, the goings on in the body. Rather, the neuromuscular processes are by themselves only the material-cum-efficient causal aspect of a single event of which my thoughts and intentions are the formal-cum-final causal aspect. There is simply no way fully and accurately to describe the one event in question without making reference to each of these aspects. Just as there is no such thing as the matter of a stone or tree apart from the form of a stone or tree, there is no such thing as the “physical” side of my action apart from the “mental” side. To make reference to the “physical” side alone would simply be to leave out half of the story, and indeed the most important half, just as describing the word “cat” in a way that makes reference to the shapes of the letters, the chemicals in the ink in which it is written, and so forth, while never saying anything about the meaning of the word, would leave out the most crucial part of that story.

As psychologist Jerome Kagan emphasizes in his recent book An Argument for Mind (my review of which can be found here) the trouble with trying to pick out some particular pattern of neural or other physiological events and identify some mental event with it (or in any other way attempt entirely to explain the mental in terms of the physiological) is that the same physiological pattern can underlie different mental events and the same mental event can be associated with different physiological patterns. This is a problem well-known to students of the history of the mind-brain identity theory (cf. Davidson’s anomalous monism), though it seems to me that many philosophers do not appreciate just how deep the problem goes, and how thoroughly devastating it is to materialism. As writers like James F. Ross have argued, at least some of our mental states are determinate in a way that no material process or set of processes can be even in principle, so that the hope of making mental states out to be identical with or supervenient upon physical states is an illusion. Without formal and final causes, it is inevitable that the project of assigning some specific, determinate mental content to this or that material substrate will come to grief. (Thus does the interaction problem arise in a new form even for materialists themselves, under the guise of the “mental causation problem.”)

Hence there can, on an Aristotelian-Scholastic view, be no question of some uniquely identifiable set of physiological events with which an independently identifiable set of mental events needs somehow to be correlated in efficient causal terms. There is just the one event of writing the blog post, of which the formal, material, efficient, and final causal components are irreducible aspects. The question of "interaction," in the relevant sense, simply cannot even get off the ground. As is so often the case with objections raised against modern defenses of traditional philosophical views (such as theism and natural law ethics), the interaction problem facing Cartesian forms of dualism arises precisely because these forms of dualism are modern, precisely because they take on board certain modern (especially mechanistic and/or nominalistic) assumptions which they (like theists and natural law theorists) ought instead to repudiate.

I have said much more about all of this in Philosophy of Mind and (especially) The Last Superstition, and I will say more about some of these issues in further posts to come in my series on brief arguments for dualism. The point for now is just to highlight that what we have here is yet another respect (among a great many others that I describe in detail in TLS) in which the early modern philosophers’ transition away from Aristotelianism to a mechanical understanding of nature constituted not an advance but a regression, a willful forgetting of crucial distinctions and categories the drawing and elucidation of which had been one of the great achievements of Scholasticism, and a conceptual impoverishment that inevitably created problems rather than solved them. The interaction problem was by no means the least, or last, of these problems.