Problem of universals

The philosophical question of whether properties and kinds shared by multiple things exist independently, only in particular things, or only in minds that recognize them.

Platonism: The view that abstract entities exist independently of physical things and human thought. Universals exist independently as abstract realities in this account.
Theory of Forms: Plato’s account of eternal, intelligible Forms that particular things imperfectly exemplify. Plato’s Forms provide a classic account of independently existing universals.
Universal (metaphysics): A repeatable property, relation, or kind that can be instantiated by multiple particular things. The dispute turns on whether entities of this kind exist.
Natural kinds: Categories whose membership is grounded in nature rather than solely in human convention. Whether kinds are real universals shapes how natural classifications are understood.
The One Over Many: A metaphysical problem asking what explains one property or kind being predicable of many things. It states the central explanatory puzzle behind realism about universals.
Aristotelian realism: The view that universal features exist in particular things and are understood through abstraction. It locates universals in instances rather than in a separate realm.
Aristotle: An ancient Greek philosopher whose works shaped logic, metaphysics, biology, and ethics. His account located form in individual substances rather than separate Forms.
Particular: An individual entity that exists at a specific place and time and is not multiply instantiated. Particulars are the individual things whose shared features need explaining.
Scientific realism: The view that successful scientific theories describe a mind-independent world, including unobservable entities. Realism about universals bears on whether scientific properties are discovered or imposed.
Whitehead's problem: A puzzle about how one and the same property can be wholly present in many distinct things. The case of shared whiteness makes the repeatability problem vivid.

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