THOMAS AQUINAS AND THE UNITY OF SUBSTANTIAL FORM

John F. Wippel

Let me begin by specifying the theme of this essay a little more pre- cisely than its title indicates. In this study I intend to concentrate on Thomas Aquinas’ views on the unity of substantial form in human beings, and then on the controversy that arose concerning this doc- trine. This controversy seems to have arisen during the final years of Thomas’ lifetime, and even more so in the years and decades imme- diately following his death in March, 1274. So true is this that this theory was condemned in England by successive Archbishops of Can- terbury in 1277, 1284 and 1286. And in Paris, this theory, at least as it was defended by Giles of Rome, was censured in March, 1277 by an assembly of members of the Theology Faculty convened by the Bishop, Stephen Tempier. After we have considered Aquinas’ position in itself, more will be said below about these ecclesiastical interventions insofar as they shed some light on the adverse reactions to his theory during his own lifetime. As is well known, Thomas correlates the soul and body of a human being as substantial form and prime matter. In doing so he was obviously heavily influenced by Aristotle’s theory of the matter-composition of all corporeal entities as he had worked this out in both his Physics and Metaphysics. And in his De anima, Aristotle applies this to the relationship between soul and body in living entities including human beings. Therefore, in order to appreciate Aquinas’ account of the rela- tionship between soul and body, it will be helpful to recall a few points about his general metaphysical views on the matter-form relationship in corporeal entities.

I. Matter and Form in Corporeal Entities

At the very beginning of his career, in his youthful De principiis natu- rae (ca. 1252–1256) Aquinas explains the distinction between potency and act. That which can exist but does not is said to exist in potency. That which already exists is said to exist in actuality. But Thomas 118 john f. wippel immediately distinguishes two kinds of existence (esse): the essential or substantial existence of a thing (esse simpliciter), such as that of a human being, and accidental existence (esse secundum quid), such as for a human being to be white. Corresponding to these two ways in which existence may be realized, that is, as substantial or as accidental, are two ways in which something may be in potency, that is, it may be in potency to substantial existence or to accidental existence. Both that which is in potency to substantial existence and that which is in potency to accidental existence may be referred to as matter. But the kind of matter which is in potency to substantial existence is referred to as matter “from which” (ex qua) something is made, while the kind of matter that is in potency to accidental existence is referred to as matter “in which” (in qua) something inheres. The first kind of mat- ter is often referred to as prime matter, while the second kind can be identified with a substantial subject or substance. And this points to a further distinction between them. A subject or substance does not derive its substantial existence (esse) from the accidents which inhere in it, but matter taken in the first sense prime( matter), does receive its substantial existence (esse) from the substantial form that informs it.1 Given this, one often finds Thomas writing that form ‘gives’ esse to matter when he is referring to substantial form. But to return to our text from the De principiis naturae, Thomas then correlates what he has said so far with two kinds of change. Because generation is a motion towards a form, whether substantial or accidental, there are two kinds of change, substantial change and accidental change. In substantial change a substantial form is intro- duced into prime matter, and so something is said to be made in the absolute or unqualified sense. In accidental change an accidental form is introduced into a substantial subject. Thus if a dog is generated, one has substantial change; but when the dog’s quantity increases, one has accidental change. This also applies to the loss of a form. If a substance such as a dog collides with a train, the dog loses its substantial form and undergoes another kind of substantial change, that is, corruption. So too, if the dog loses some weight, it undergoes a less drastic kind of corruption, accidental change. (To put this another way, generation and corruption in the absolute sense are restricted to substances, while

1 Cf. De principiis naturae, § 1 (ed. Leonina), vol. 43, p. 39 (ll. 1–46); J. F. Wippel, The Metaphysical Thought of Thomas Aquinas: From Finite Being to Uncreated Being, Washington (D.C.) 2000, pp. 296 sq.