Problem of Universals

The problem of universals is an ancient problem in metaphysics about whether universals exist. Universals are general or abstract qualities, characteristics, properties, kinds or relations, such as being male/female, solid/liquid/gas, or a certain colour, that can be predicated of individuals or particulars, or that individuals or particulars can be regarded as sharing or participating in. For example, Scott, Pat, and Chris have in common the universal quality of being human or humanity. While many standard cases of universals are also typically regarded as abstract objects (such as humanity), abstract objects are not necessarily universals. For example, numbers can be held to be particular yet abstract objects.

The problem of universals is about their status; as to whether universals exist independently of the individuals of whom they can be predicated or if they are merely convenient ways of talking about and finding similarity among particular things that are radically different. This has led philosophers to raise questions like, if they exist, do they exist in the individuals or only in people's minds or in some separate metaphysical domain? Questions like these arise from attempts to account for the phenomenon of similarity or attribute agreement among things. For example, living grass and some apples are similar, namely in having the attribute of greenness. The issue, however, is how to account for this and related facts.