Universals — That which can be predicated of many individuals or be present in many particulars at once, as opposed to the particular, which is single and unrepeatable. Terms such as “human,” “white,” or “triangle” seem to name something common to countless distinct things: what makes Socrates and Plato equally human? The central question, known as the problem of universals, asks whether such general terms correspond to any real entity or are merely words. The classic formulation reached the Latin Middle Ages through Porphyry’s Isagoge, commented upon by Boethius, which asked whether genera and species exist in reality or only in the understanding. Three major positions structure the debate. Realism holds that universals have an existence of their own: for Plato they are the Forms or Ideas subsisting apart from sensible things, a line inherited by the Augustinian tradition and by Anselm of Canterbury. Nominalism denies such existence and reduces universals to names (nomina) or linguistic signs we apply to similar things, a view associated with William of Ockham and his principle of economy. Between the extremes, the conceptualism of Peter Abelard maintains that universals are neither things nor mere words, but concepts formed by the mind from what particulars share in common. The theme runs through ancient and medieval metaphysics and remains alive in contemporary analytic philosophy, tied to questions about properties, natural kinds, and the status of abstract entities.
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