Aristotle's theory of universals

Aristotle's theory of universals is one of the classic solutions to the problem of universals. Universals are types, properties, or relations that are common to their various instances. In Aristotle's view, universals exist only where they are instantiated; they exist only in things (in Latin, it is said they exist in re, which means "in things"), never apart from things. Furthermore, Aristotle said that a universal is identical in each of its instances. So all red things are similar in that there is the same universal, redness, in each thing. There is no Platonic Form of Redness, standing apart from all red things; instead, each red thing has a copy of the same property, redness.