 Realism and nominalism were the two major theoretical alternatives in the later Middle Ages concerning the reality and kinds of general objects, and the status and mutual relationships of the basic items of the world (individual and universal substances, individual and universal accidents) as well as their connection to language. Realists believed in the extra-mental existence of common natures (or essences); nominalists did not. Realists held that Aristotle’s table of categories was first of all a partition of things grounded on ontological criteria and only secondarily a classification of (mental, written, and spoken) terms, and therefore that the world is divided into ten kinds of things (in a broad sense of ‘thing’), not one of which can be reduced to any other. Nominalists maintained that the division into ten categories was a partition of terms on the basis of semantic criteria, and that there are only two or three real categories (substance and quality, and perhaps quantity too). Realists believed that thought was linguistically constrained by its own nature, and accordingly they considered thought to be related to reality in its elements and constitution, and deemed language, thought, and external reality to be of the same logical coherence. Nominalists sharply distinguished between things as they exist in the external world and the various forms by means of which we think-of and talk-about them, since for them our (mental, spoken, and written) language does not reproduce the world, but merely regards it, as our (mental, spoken, and written) language and the world are logically independent systems.