Medieval thinking about relations is historically as well as theoretically embedded within the larger context of the Aristotle’s theory of categories. This basic fact is important, both because it had a profound impact on the way medieval philosophers thought about relations and because a great many of the questions that come up in medieval debates arise more or less directly out of the basic commitments of that theory. Three commitments are particularly important. First, relations make up a distinct category, the category of relations. Accidents are characterized by being in a subject, and it is this feature that distinguishes them from substances. Second, relations are accidents. Third, as with all other categories, relations come in two kinds: universals and particulars. On the standard medieval analysis a relation is a sort of link or being toward that a single substance has, not all by its lonesome, but with respect to some other substance.