WHETHER IT IS INCOMPATIBLE FOR TWO ACCIDENTS, DIVERSE ONLY IN NUMBER, TO BE SIMULTANEOUSLY [PRESENT] IN THE SAME SUBJECT OWING TO THEIR INDIVIDUALITY (individuationem)
1. There are two ways in which accidents [present] in the same subject may differ only in number, namely, simultaneously or only successively. Both [ways] are under dispute, but we discuss only the first in the present Section.1
2. The first opinion denies that not only accidents of the same species but also of diverse species, provided they be contained in the same proximate genus, can be simultaneously [present] in the same subject. It may be seen in St. Thomas, [ Summa theologiae ] I, q.85, a.1, where he says: "It is impossible for the same subject to be perfected simultaneously by many forms of one genus and of diverse species, just as it is impossible for the same body in the same respect to be simultaneously colored by diverse colors or shaped by diverse shapes."3 Moreover, in q.8 of On Truth, a.14, he states it concerning forms existing in perfect act.4 Thomists commonly adopt this explanation, and in this way they solve the difficulties concerning the many intelligible or sensible species contained within the same proximate genus -- such as the species of man and horse -- and existing simultaneously in the same power. [They] also [solve the difficulties] concerning two sciences, for example, or two moral or theological virtues,5 which, although differing in species and contained under the same proximate genus, could be simultaneously [present] in the same power, even with perfect intensity. For they say that these and similar [things] are simultaneously [present in the same subject] only in incomplete act, because they are simultaneously [present] in it only in first act or in habit, not in second act.