Universal (metaphysics)

In metaphysics, a universal is a type, a property, or a relation. The noun universal contrasts with individual, while the adjective universal contrasts with particular or sometimes with concrete. The latter meaning, however, may be confusing since Hegelian and neo-Hegelian (e.g. British idealist) philosophies speak of concrete universals.

A universal may have instances, known as its particulars. For example, the type dog (or doghood) is a universal, as are the property red (or redness) and the relation betweenness (or being between). Any particular dog, red thing, or object that is between other things is not a universal, however, but is an instance of a universal. That is, a universal type (doghood), property (redness), or relation (betweenness) inheres a particular object (a specific dog, red thing, or object between other things).

Platonic realism holds universals to be the referents of general terms, i.e. the abstract, nonphysical entities to which words like "doghood", "redness", and "betweenness" refer. By contrast, particulars are the referrents of proper names, like "Fido", or of definite descriptions that identify single objects, like the phrase, "that apple on the table". By contrast, other metaphysical theories merely use the terminology of universals to describe physical entities.

The problem of universals is an ancient problem in metaphysics concerning the nature of universals, or whether they exist. Part of the problem involves the implications of language use and the complexity of relating language to ontological theory.

Most ontological frameworks do not consider classes to be universals, although some prominent philosophers do, such as John Bigelow.

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