The Thomist: A Speculative Quarterly Review

AQUINAS ON THE RELATIONSHIP BETWEEN DIFFERENCE IN KIND AND DIFFERENCE IN DEGREE MUCH HAS BEEN written about the roles of both genera a:p.d accidents in the metaphysics and epistemology of St. Thomas Aquinas. But no one has heretofore drawn out the implications of a comparison of genera and accidents for St. Thomas's very important theory of the relationship between difference in kind among things and difference in degree among things. Genera and accidents can most fruitfully be compared in terms of generic and accidental concepts since the unity of the genus is conceptual only. A genus cannot be one in the way that, say, a species is one, i. e., in terms of a formal identity in things, since in things " generic forms " exist only as specified in various diverse ways.1 The relationship between a generic concept and things is nearly the contrary of the relationship between a concept of an accident and things. We are able to know many things by one generic concept because of its indeterminacy; all of the things known by a generic concept are more determinate than is the concept. Animal nature, for example, is perfected and fulfilled as it exists in things-various kinds of animals. However , with accidents the concept is more determinate than are most of the things to which it applies. Most things are not completely white, but our concept white is a likeness of perfect whiteness, or nearly perfect whiteness, against which things having various degrees of whiteness are measured, thus enabling us to determine just how white something is. 1 See Armand Maurer, "St. Thomas and the Analogy of the Genus," New Scholasticism, 1955 (29), 181. Cf. F. F. Centore, "A Note on Diversity and Difference," THE TnoMIST, XXXVI (July, 1972), 472-482. 116 AQUINAS ON DIFFERENCE IN KIND AND DEGREE 117 The difference in relationships between generic concepts and things and between accidental concepts and things reflects a difference in things. Animal cannot exist except as a particular kind of animal, but perfect whiteness can exist apart from all the degrees of whiteness (although it cannot exist apart from something which is perfectly white) . White things are not equally white, but all animals are equally animals. The difference in things between genera and accidents can be traced to their different relationships to substance. Using non-Thomistic terminology, the relationship between a genus and substance can be called perfecting determination, which produces differences in kind. The different kinds, or species, of animals each perfect animal nature in their own ways. The relationship between accidents and substance can be called non-perfecting determination, which produces differences in degree . White things, in varying degrees, subtract from the perfection of pure whiteness.2 Differences in kind and differences in degree are fundamentally distinct kinds of difference and are the ground for fundamentally distinct kinds of universals (that is, concepts related to things as a one is related to a many), each generated by its own type of cognitive process. A generic concept can be a universal because the mind has made it indeterminate in relation to things, while a concept of an accident can be a universal because the mind has produced, from imperfect instances, a perfected image, or representation, which can be related to things as a standard of measurement. Although difference in kind and difference in degree are distinct kinds of difference, according to St. Thomas, one is more fundamental than the other and is, in a sense, a cause of it. Difference in degree is more fundamental than difference in kind. Difference in kind is found most prominently in genera. : The relationship between accidents and substance can properly be called nonperfecting determination only from the perspective of accidents, since substance is perfected by certain accidents. But an accident itself is usually not perfected by a substance in that the accident is, in varying degrees, instantiated imperfectly. 118 RALPH W. CLARK Things differing in a genus differ in kind, as we have noted. However, they also differ in degree: In every genus there is something most perfect in that genus, by which all the other members of the genus are measured: everything is shown to be...