Aristotle's theory of universals

Aristotle's Theory of Universals is Aristotle's classical solution to the Problem of Universals, sometimes known as the hylomorphic theory of immanent realism. Universals are the characteristics or qualities that ordinary objects or things have in common. They can be identified in the types, properties, or relations observed in the world. For example, imagine there is a bowl of red apples resting on a table. Each apple in that bowl will have many similar qualities, such as their red coloring or "redness". They will share some degree of the quality of "ripeness" depending on their age. They may also be at varying degrees of age, which will affect their color, but they will all share a universal "appleness". These qualities are the universals that the apples hold in common.

The Problem of Universals asks three questions. Do universals exist? If they exist, where do they exist? Also, if they exist, how do we obtain knowledge of them? In Aristotle's view, universals are incorporeal and universal, but only exist only where they are instantiated; they exist only in things.^[1] Aristotle said that a universal is identical in each of its instances. 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. For the Aristotelian, knowledge of the universals is not obtained from a supernatural source. It is obtained from experience by means of active intellect.^[1]