Friday, October 19, 2012
How mind-body interaction in Aquinas is not subject to Cartesian problems
So, Descartes famously establishes a mind-body dualism in his Meditations on First Philosophy. He divides substance into two species: res extensa and res cogitans (extended stuff and thinking stuff). Res extensa is material, extended, divisible, etc. Res cogitans is immaterial, non-extended, simple, etc. A human being is primarily a cognitive substance united to an extended body. But given the total diversity of res cogitans and res extensa, it becomes very difficult for Descartes to explain how the two could interact causally. How can changes in the body be communicated to the soul (e.g. sensation), and how can motions of the soul be communicated to the body (e.g. in willing)? What mediates this interaction? Descartes realizes this is a problem, but his solution is famously inadequate. He says that the locus of interaction between body and soul is the pineal gland in the brain, and the two interact by the exchange of pressures on a certain membrane. Now, obviously this doesn't work because by claiming that the soul can exert pressure on a membrane he is effectively predicating a spatial, material action of a non-spatial, immaterial substance. And so this begs the question: how can the soul move the pineal gland in the first place? And we're back where we started. This problem continues to haunt mind-body dualism. (Thus the need for Cartesian duellists to defend the honor of the system. Dylan Morris)
Now, in Aquinas, there is at first glance a similar duality between soul and body: the body is material and the soul is subsistent and immaterial. Some actions of the human are referred to the body (e.g., digestion, imagination), and some to the immaterial soul (e.g. willing, intellection). In fact, a lot hinges on the fact that certain functions of the human person cannot be cogently described as acts of a physical organ (proofs of the immateriality and hence immortality of the soul, notably). But consider the following situation. Suppose you're walking in the woods and you come across an unusual flower, one that you haven't seen before. According to the Thomist, the process by which you're able to know proceeds causally as follows: first the flower exists and has its own form, but then by the action of the sun illuminating the flower, it is capable of communicating its form as a visible image to your eye. The image on the retina which conveys the form is then received by the common sense, and this datum elicits a phantasm in the imagination. All of this, according to the thomist, happens in physical organs (your eye and brain). The next step involves a shift: the agent intellect renders the phantasm intelligible and abstracts universal content from it, which is then impressed on the passive intellect, by which you are able to apprehend and make judgments about the universal attributes of the flower.
The problem one might pose is this: in the interaction between the corporeally situated faculty of imagination and the immaterial/spiritual faculty of understanding, there seems to be some leap. What was in the person corporeally is suddenly shifted over to something incorporeal: a material fact has some effect on an immaterial thing. This seems to cause the same difficulties as Descartes faces in his dualism: how can we explain the communication of motion from an immaterial substance to a material one and vice versa? The thomist might weakly reply that the immaterial soul is the form and life of the body, and thus has a substantial unity with the corporeal functions of the person that Descartes ghost-in-machine anthropology doesn't allow for. But even so, it remains true that the intellectual faculties are not situated in an organ, and thus it seems impossible to explain interaction between the material and the immaterial processes here.
The solution to the problem is to remember that all material beings are, according to St. Thomas, a composite of matter and immaterial form. The form of a material thing is not subsistent, i.e., it does not have its own being apart from the composite in which it exists, but it can be communicated to another thing inasmuch as that thing is capable of receiving it. (Whatever is received is received according to the mode of the receiver.) So, for example a piece of film is capable of receiving the form of a flower in a certain way, or a piece of canvas in another way. What is communicated here isn't a bit of the flower, but its form: you don't have to cut off a petal to take a picture of the flower, but even so something of what the flower is comes to be in the film. What is communicated is immaterial. But in this case the cartesian problem vanishes, because there is no longer a communication of material stuff to immaterial stuff: the interaction is not causal after the fashion of billiard balls bumping into each other (how could a brain bump into a soul? what would mediate this interaction?), but in the broader understanding of causation as the communication of forms from one agent to another. In the line of causation from the form of the flower subsisting in it materially to the image in the eye and the phantasm in the brain to the abstract from in the intellect, what is communicated is immaterial (the form) and that to which it is ultimately communicated (the passive intellect) is also immaterial. Hence hylomorphism seems to do away with one of the most crippling problems of Cartesian mind-body dualism.