Platonic realism

In Platonic realism, universals exist ``in a realm'', that is separate from space and time. According to this belief, universals are not ideas in someones mind, they are not mental entities at all. One way to see Plato's universals is as ``archetypes'', as original models, and particular objects are copies of those models. A specific banana is a copy of banananess, the specific yellow of a yellow car is a copy of yellowness. Another way objects and universals might be related is that objects ``participate'' in the universals, or the universals are ``inhered'' in the objects.

In Platonic realism, some universals are not instantiated at all, although they could be instantiated. Exactly how particular objects instantiate a universal is a basic problem of Plates theory.

If we think of yellowness in general, we think of the universal ``yellowness'', not of a particular yellowness of some object. But how the concept of ``yellowness'', an entity that exists neither in space nor in time, came to our mind, is another problem that has to be solved in the theory of Platonic realism. Plato's answer was quite simple: We were all born with ``a priori'' knowledge of a wide variety of concepts.

Despite a lot of criticism, Platonic universals seem to capture the meaning of general term, like ``yellowness'' or ``banananess'', well. When we speak of something yellow, it is convenient to think of it as something outside of space and time, but which has a lot of instances.