Problem of universals

The problem of universals is an ancient question from metaphysics that has inspired a range of philosophical topics and disputes: "Should the properties an object has in common with other objects, such as color and shape, be considered to exist beyond those objects? And if a property exists separately from objects, what is the nature of that existence?"

Universals are qualities or relations found in two or more entities. As an example, if all cup-holders are circular in some way, then circularity may be considered a universal property of cup-holders. Similarly, if one has a set of seven red and three blue balls, it would seem that though the set comprises ten separate entities (balls), there are only two colors therein—each being shared by multiple balls. Many properties can be universal: being human, red, male or female, liquid or solid, big or small, etc.

The problem of universals relates to various inquiries within metaphysics, logic, and epistemology, dating from as far back as Plato and Aristotle, in efforts to understand how the same single property can be (at least apparently) shared across multiple, non-identical objects. Philosophers agree that human beings can talk and think about universals, but disagree on whether universals exist in reality beyond mere thought and speech.