  The distinction between real relations and relations of reason has a number of important consequences for the development of medieval theories of relations. For one thing, it enables philosophers to introduce a number of refinements and distinctions within the category of relations. By the mid-thirteenth century, for example, it becomes common to say that the category of relations is unique in allowing mere beings of reason among the things signified by its terms. To quote from Aquinas who is representative in this regard: