Finally, universals and particulars, like causes and effects, can be considered in three ways. Causes and effects are considered, first, as certain things—for example, the sun as sun and gold as gold; second, as causes or effects—for example, the sun as producing gold and gold as produced by the sun; and third, in their mutual relation, one as cause to effect and the other as effect to cause. The same applies to universals and particulars. In the first way they are considered as things, with no account taken of their universality or particularity, as animal insofar as it is animal and man insofar as he is man. In the second, they are considered as universals or particulars. For in animal, being animal is one thing, and being common to man and beast is another: being animal belongs to every animal, whereas being common to man and beast belongs only to animal taken precisely, that is, without consideration of any contracting difference. Likewise, in man, being man—which belongs to human beings alone—is one thing; being a species subjected to animal—which is shared with other animals—is another. In the third way they are considered insofar as they stand in mutual relations to one another: universals as common wholes, and particulars as parts subjected to them.
In the first way, all sciences and arts discourse about universals, as was said at the beginning—not all about all of them, but different sciences about different universals. Physics treats all the genera of animals and plants; moral science treats all the forms of virtues and vices; medicine treats the common differences of all diseases and treatments. In the second and third ways, however, it belongs only to first philosophy and Dialectic to treat universals and particulars. Being universal and particular, and the relations between universals and particulars, are common features of things; they belong no more to the things considered by one science than to those considered by another. They must therefore belong to sciences concerned with all things, such as first philosophy and Dialectic alone—to leave aside sophistry, which is designed not for truth but for deception. Yet the two sciences consider them in different ways. First philosophy treats them as common features of things; Dialectic treats them insofar as knowledge of them contributes to reasoning and its common use. Dialectic’s teaching—and even its practice—depends remarkably on considering universals and particulars and the relations by which universals are related to particulars, and particulars in turn to universals. The relations themselves, however, are held to be less important in both first philosophy and Dialectic than the accounts of universals and particulars explained above.
But three things are considered in the definitions of the universal: the unity of universal things, their aptitude to be in many, and their aptitude to be predicated of many. Although both sciences treat all these matters in some way, it must be understood that the first philosopher, as part of his proper inquiry, discusses only the first two, while the dialectician discusses only the third. The first philosopher treats general modes of predication only so that, guided by them, he may discover general modes of being; he discusses the method of definition only to teach many things about the quiddity and nature of things. The dialectician, by contrast, presents—or rather receives from the first philosopher—certain accounts of the modes of being of things, and of their unity and distinction, in order to gather all the modes of predicating and reasoning. The same judgment applies to the three corresponding conditions of particulars: their unity and their aptitude to be subjected to their universals and to serve as subjects in predication.