- Few notions are more central to Aquinas’s thought than those of matter and form. Although he invokes these notions in a number of different contexts, and puts them to a number of different uses, he always assumes that in their primary or basic sense they are correlative both with each other and with the notion of a “hylomorphic compound”—that is, a compound of matter ( hyle ) and form ( morphe ). Thus, matter is an entity that can have form, form is an entity that can be had by matter, and a hylomorphic compound is an entity that exists when the potentiality of some matter to have form is actualized. What is more, Aquinas assumes that the matter of a hylomorphic compound explains certain of its general characteristics, whereas its form explains certain of its more specifi c characteristics. Thus, the matter of a bronze statue explains the fact that it is bronze, whereas its form explains the fact that it is a statue. Again, the matter of a human being explains the fact that it is a material object, whereas its form explains the specifi c type of material object it is (namely, human ).
- Consider, therefore, one of Aquinas’s favorite examples of change—namely, one by which a statue is made from a lump of bronze. To fill out this example, let us suppose our lump starts off being spherical but is later melted down and recast as a statue. In that case, we will have a situation that, for the sake of future reference, we can represent as follows (using a circle to stand for our sphere, a square to stand for our statue, and a dotted arrow to represent the direction of time):
- As this diagram is intended to make clear, our example involves a process that begins with an entity that can be characterized in one way (namely, as a sphere) and ends with an entity that can be characterized in another way (namely, as a statue). In this respect, Aquinas thinks, our example is perfectly representative of all change. We might put the point by saying that, for him, change essentially involves the temporal succession of distinct entities—or, in terminology closer to his own, the “coming-to-be” of one thing and the “passing-away” of another. Thus, if we want to represent our statue example, as Aquinas himself is thinking of it, we cannot merely appeal to the temporal succession of distinct entities. On the contrary, we must introduce some complexity into such entities, so as to indicate that they not only (a) involve distinct elements (and hence are distinct) but also (b) share a common constituent (and hence overlap). Since Aquinas himself describes the change in terms of the same bronze having different shapes at different times, we can represent his understanding more accurately as follows:
- [9:59 PM]As all of this suggests, change for Aquinas just consists in the generation and corruption of hylomorphic compounds (or compounds of potentiality and actuality). For the sake of clarity, we can represent this general account of change as follows:
- Change: Change happens when something (matter) exists at one time with one characteristic (form), and then later exists with a different characteristic (a different form). Matter and Form: Matter is the basic substance, and form is the characteristic or shape it takes. For example, a piece of clay (matter) can be shaped into a cup (form). Hylomorphic Compound: This is the combination of matter and form. When matter takes on a form, it creates a compound entity. Realism: Aquinas believed in a realistic view of matter, form, and compounds. He thought all three are necessary to explain any change. Matter can exist without a specific form, and both matter and form are needed for compounds to exist. Identifying Matter, Form, and Compounds: Since matter can exist without a specific form, and compounds need both matter and form, they can’t be the same thing. Matter and form are distinct but necessary for the existence of compounds. Realism in Change: Aquinas’s view implies a realism about matter, form, and compounds. Some suggest he might not have been a realist about matter in certain substantial changes, but if his account applies to all changes, then he must have believed in realism about matter in all changes.
- Types of Matter, Form, and Change
- Aquinas thinks that all of the changes we have been focusing on so far belong to a single type—namely, ones involving a substance (which plays the role of matter) changing with respect to one of its contingent properties or accidents (which plays the role of form). For obvious reasons, he calls changes of this type “accidental change,” and he calls the compounds thereby generated or corrupted “accidental compounds (or unities). Although Aquinas regards many familiar examples of change as accidental, he denies that all of them are. On the contrary, he thinks there are also familiar examples of substantial change—that is, changes by which substances themselves are generated or corrupted. Aquinas’s favorite example here is the change by which a human being (such as Socrates) is generated from sperm and menstrual blood (or as we now know better, sperm and ova). In order to highlight the connection between Aquinas’s understanding of substantial change and his account of change in general, let us pretend for the moment that he thinks of human beings as being generated not from two things (namely, sperm and menstrual blood or ova), but rather from a single thing (namely, a fertilized egg or zygote). In that case, we can represent Aquinas’s example of substantial change as follows:
- Indeed, we can just define the difference between substantial and accidental change in terms of whether the enduring subject of change can be so characterized. More precisely:
- Matter, Form, and Individuation
- Suppose, therefore, our statue had been generated not from a single sphere, but from several smaller spheres. Or again, suppose the corruption of our zygote resulted in the generation not of a single human being, but of twins—say, Romulus and Remus. In either case, note that on the “many” side of the change we have multiple objects belonging to the same kind, and hence relations of sameness and difference holding between distinct individuals. These relations, however, obtain at a time rather than over time, and hence could obtain even in the absence of change. Moreover, instead of involving sameness of subject and difference of characterization , these relations involve difference of subject and sameness of characterization. Aquinas appeals to matter and form to explain the relevant relations of sameness and difference—though, of course, this time it is form that explains the sameness and matter that explains the difference. For the sake of clarity, we can contrast the different roles Aquinas assigns to matter and form in different contexts using the following chart:
- Although Romulus will fill some region or other solely in virtue of having prime matter, and his distinct prime matter may well put some restrictions on the size of this region, his precise extension cannot be determined apart from certain of his accidental or quantitative properties—what Aquinas calls his “determinate dimensions” (dimensiones deteriminatae vel terminatae ) or “dimensive quantities” ( quantitates dimensivae ). And, obviously, since Romulus himself cannot exist without some dimensions or other, the same will be true of his prime matter. Chart:
- Quantity, Individuality, and The Individuation of Forms
- If individuation, for Aquinas, involved nothing more than explaining the distinction of material objects, we could perhaps leave our discussion here. But, in fact, this is not the case. To see why, consider Romulus and Remus again and note that they are not merely distinct entities, but distinct individuals . The qualifi cation is important because, as we have seen, there are entities (e.g., Romulus’s and Remus’s respective prime matter) which are distinct but nonindividual. But, then, how are we to account for the individuality (as opposed to distinction) of Romulus and Remus? Obviously, we cannot account for it in terms of their prime matter, since as we have just noted, it is nonindividual. But neither can we account for it in terms of their substantial form, since this is something they share in common. But if we cannot account for Romulus’s and Remus’s individuality either in terms of their (nonindividual) prime matter or in terms of their (common) substantial form, how can we account for it? Chart:
- Conclusion
- This completes our examination of the two main contexts in which Aquinas develops his notions of matter and form—his theory of change and his theory of individuation. In each case, as we have seen, Aquinas invokes matter and form to account for certain relations of sameness and difference holding between distinct individuals. In each case, moreover, he is able to do so because he thinks of matter and form as distinct entities that both serve as constituents of larger wholes (namely, hylomorphic compounds) and explain certain of their general and specifi c characteristics. There is much more that could be said about Aquinas’s understanding of matter and form, especially in other contexts such as theology or logic. But we have already seen enough, I think, to appreciate the essential aspects of these notions in their primary or basic sense, and hence to have a basis for understanding the further uses to which Aquinas puts them.
