The recent discussions at Vallicella’s website got me thinking of this again. Roughly, there are two opposing schools of thought in the philosophy of mind: materialism in its various forms, and dualism—usually substance dualism, something akin to Descartes view given in his Meditations. One version of dualism that has been virtually ignored since Descartes (along with other early-modern thinkers) rejection of it is hylomorphic dualism (or Thomistic dualism).
Substance dualists seem to find the view as bizarre as materialists do, but this, I think, is due to the general rejection of the metaphysics that underlie it. Hylomorphic dualism derives from hylomorphism (from the Greek words hyle, meaning “matter,” and morphe, meaning “form”), the view that all material objects are composites of matter and form. Matter and form unite to form a substance, the only things that exist in their own right (a ball, this cat, this tree, this computer, etc.). Some substances (according to hylomorphism) are entirely immaterial, but these unique and I shall set them aside for now. Physical substances however, are matter form composites. The form of an object just is its organizational structure. It is the precise arrangement or configuration of the material parts of a thing into a certain whole. The substantial form in turn speaks of the configuration of material parts of a thing so that that thing is (actually) what it is. So form is the answer to the question “What is it?”—Something abstract and universal. Now because a material object would not be the kind of thing it is without its specific form, no material thing can be composed simply of matter. In fact, matter can only be distinguished from form logically. So distinguished, it is prime matter.
One consequence of this view is that a proper understanding and explanation of material entities cannot be approached without appeal to formal and final causes. When someone asks ‘what’s a hammer?’ The hearer ordinarily takes the question as an inquiry into the things nature (formal cause), and its end (final cause). ‘Well it is such-and-such a thing, used for doing such-and-such,’ is the common response. Now early-modern thinkers emphatically rejected any notion of substantial forms. Descartes, in particular did not hesitate to voice his suspicion:
If you find it strange that I make no use of the qualities one calls heat, cold, moistness, and dryness…, as the philosophers [of the schools] do, I tell you that these qualities appear to me to be in need of explanation, and if I am not mistaken, not only these four qualities, but also all the others, and even all of the forms of inanimate bodies can be explained without having to assume anything else for this in their matter but motion, size, shape, and the arrangement of their parts.
For Descartes, a proper understanding of nature does not require any notion of substantial forms and the implied notions of formal or final causes. Instead, identity, motion, and change in material entities can be understood in purely physical terms. Material and efficient causes are sufficient—hence, of course, his purely mechanistic account of the universe in Le Monde. But Descartes aside, what I find interesting about hylomorphism is its strictly commonsensical account of the world around us. When a child strolls into his father’s room and sees a guitar on the table, he asks “what’s that?” The appropriate response is “that’s a guitar.” But the child might follow with another question, “what’s a guitar?” Here, no lecture on the physics of the wood in the guitar, or its, length, depth, sturdiness, etc., will do as an appropriate response, for the child’s question is an inquiry into the nature of guitars, and their ends. “Son, a guitar is such-and-such a thing used for doing such-and-such” would be the proper response.