What birds plunge through is not the intimate space
in which you see all forms intensified.
Dualism about ultimate kinds of things—that there are two, mental and physical—has been the dominant position in the history of philosophy, though it happens to have fallen out of favor in the last half century or so. The surviving current versions of dualism seem to be rather apologetic positions that struggle to preserve room for dualist concerns within a general monistic and materialist conceptual climate. Dualism is next in our series on ontology. Since just about every view in philosophy assumes something about "what there is" we are surveying some possibilities. Here I will hone in on what I think is the biggest problem for dualists, explaining mind and body interaction.
I think the real issue of importance—the fault line along which distinct types of dualism divide—is mental/physical interaction. (See the references below for a fuller survey of problems with dualism.) Those dualist views that differ on how they handle the problem of interaction include classic Cartesian substance dualism, epiphenomenalism, and parallelism.
Dualisms and naturalism
Monist physicalism, in its metaphysically most aggressive forms, eliminative or reductive materialism, deals with interaction straightforwardly: there is none—the interaction problem requires two types of things while these views insist there is only one and it's not mental. We covered physicalism a few meetups ago, now we focus on dualism, the theory of ultimate reality sometimes thought opposed to physicalism. Actually, the two views are not in the strictest sense opposite. Idealism (or phenomenalism, as it was called in the early 20th century), a monist theory like physicalism, is really the polar opposite of physicalism: idealism asserts that there is only one kind of thing and it is mental. Idealism leaves no room at all for physical things independent of their mark on consciousness, while dualism takes both the physical and mental worlds at face value, and tries to explain why such seemingly incommensurable worlds must co-exist. Classic (Cartesian) dualism, by contrast, is a realist position about the mental and physical: it takes it as self-evident that both the mental and physical participate equally in existence. The existence of one is supposed to be as self-evident as the existence of the other from a true dualist perspective. The mystery is how they can co-exist in relation to each other.
Classic dualism is substance dualism. Where once dualism proudly asserted there was such a thing as immaterial "substance" along side the regular stuff you can push up against, can block your line of sight, or impinge on things that can block your line of sight or push up against, etc., now the non-material is often demoted to being a property of some (relatively rare) instances of the regular stuff which is presumed to be material. The properties in question are peculiar but not in a way that conceptually differs from, say, the qualitative aspects of color or weight. Mental properties are supposed to emerge when a material substrate reaches a certain level of organization similar to the way “life” does when organic matter reaches a certain complexity. This is known as property dualism and is the majority view among contemporary philosophers who still call themselves dualists. Epiphenomenalism is the main form of property dualism. It takes mental events to be essentially side-effects of certain physical processes. Causation works in one direction: from the physical to the mental. Mental events are taken to be “real” (in some clearly diminished sense) but physically inconsequential.
Another—I would call more—“quasi-dualist” view is to take the language of dualism to be just an efficient way of talking about certain phenomena but unrevealing of any distinct aspects of the physical world, which, it is assumed, is the only world of “substance.” The language of dualism is, thus, an artifact of the way beings like us apprehend the world: this is predicate dualism. In contrast to eliminative materialist, predicate dualists believe mental talk cannot, even in principle, be cleansed from natural languages. Sciences like psychology will never be forced to dispense with mental language anymore than we need or even should stop referring to H20 as water just because we know it to be chemically so. But like physicalists, predicate dualists take all mental events to have descriptions in physical terms though there can be no psycho-physical laws. A humble dualism, to say the least.
Parallelism, the last possible view on the dualist interaction problem, asserts two independent realms of experience, mental and physical, that do not interact—though we can be forgiven for thinking they do because of their synchronization. Leibniz is probably the only major philosopher to have held this view (though it seems implicit in Spinoza and Kant). The appearance of interaction is the result of “pre-established harmony” or synchronization set up by (who else?) God. I mention it because it deserves more consideration than it usually gets—and I will argue below there are strong reasons to take something like a parallelist view as the safest dualist starting point. One can resist speculation on how the “harmony” got there while still appreciating how well the view may fit experience. Parallelism is like eliminative/reductive materialism in this one important respect: no interaction. More later about why this view might accommodate experience better than we might at first think.
It is important to note that naturalism is not a metaphysical theory competing with the likes of the above but an epistemological one about explanation. It happens to be acting as a constraint on metaphysical speculation. It claims that everything, in some sense “real,” is potentially explainable by current or future science. But what it considers “real” inclines toward the physical. The inclination is not necessary in the sense that science could still go about its business (as it has in the past) without indulging this inclination. The behavior of entities populating the physical world and the laws governing them have become sufficiently clear to some through the methods of science that it has come to seem that there is no room for non-physical "substances" interacting with them. Every effort is made to reduce or explain away apparent manifestations of non-physical phenomena. There is nothing that non-physical things might explain, a naturalist might say. And, even if there remain mysteries in the physical world, it is hard to see how appealing to non-physical things could help with their explanations. “Explanation” used in this way has become a term of quasi-scientific art.
What's the big deal about mind/body interaction?
The importance of explaining a presumed interaction often stems from concerns about what the truth of naturalism would entail for ethics. The fear is that naturalistic explanations (deterministic or not) might undermine moral responsibility. I think it's important to point out that only some conceptions of ethics are implicated here, and even those not in a very earth-shattering way. I would argue that only consequentialist theories, in fact, are affected by any naturalist determinations, and in those theories moral responsibility is not a very robust notion to begin with. Utilitarianism, for example, is largely about environmental management of a social kind. People are essentially vessels containing actual or potential (but not intrinsic) value, measured in pleasures and pains, to be managed in the same way we might seek to manage useful resources in our environment for optimal survival. “Moral responsibility” in this theoretical context is about isolating a strategic point for external intervention. “Blame” is just a first step in trouble-shooting. More than that is getting melodramatic: guilt, retribution, respect for autonomy, the rights or inviolability of persons, even the idea of “person,” etc. are only as useful as the support they offer optimal survival and no more.
It is little wonder naturalism and utilitarianism often consort. Both are well accommodated by a monist physicalist metaphysics.
But dualism is ultimately motivated by different concerns. Prior to Descartes these concerns had not always been clear or had any great need to be. For Plato, the first great dualist, it was enough that permanence seem to be worth more than mutability and the world at the edge of the senses was uncomfortably, even offensively, mutable. Materialists then were an insignificant minority. Descartes, auspiciously placed in the history modern science, made the first attempts to get clarity about the distinctness of body and mind where Plato had not been in particular need of it. Descartes commandeered the medieval notion of substance (which was originally more a logical than a physical concept, see “Note on Substance” in the full writeup) and asserted two varieties of it: mental and physical. But already, by Descartes' time, the original more neutral sense of substance was fading. In his mechanistic picture of things, it was infused with materialist meaning and this was primary. Nevertheless, he forced a generic sense on it to describe two types of substance, mental and physical. Perhaps he was not confused himself, knowing full well “substance” had become at least half-metaphorical when applied to the non-physical, but he found it a handy way of talking about the less tangible to say it was like the more tangible in that it was at least as real or as significant to us as thinking things. What he should have been clearer about was that the mental was as substantial—in the sense of significant—as the material, not that it was material-like in any way as sorting them by the same genus “substance” might make us think. Nevertheless, the suggestion that the mental is material-like has been tightly lodged in the background of philosophical discussion since.
That set us up to ask inane questions about mind/body interaction.
1. Material substances interact, right?
2. All substances can interact.
3. Mental things are substances, too, right?
4. Then mental and material substances can (and so must) interact!
Well, then, how?... And no easy answer forthcomes. Ergo, we have a problem: mind/body interaction.
Why insist on interaction?... for my view, read the full writeup here or at least glance at this one page graphic presentation if you are really short on time and want to be provoked...
A short, clear discussion and map of the various positions on the philosophy of mind is offered here by John Danaher (paraphrasing a chapter of William Jaworski). The position I end up taking is not quite on this map—though, I suppose, it might fall under the last of the non-standard theories, “Mind-body Pessimism.” But “pessimism” seems to imply “disappointment” which does not follow from my view.
An excellent survey of the problems philosophers have had trying to account for mental causation by David Robb and John Heil.
A sympathetic overview of dualism by Howard Robinson.
Dean Zimmerman summarizes the arguments against substance dualism in “Dualism in the Philosophy of Mind”.
Dale Jacquette makes a case for property dualism.