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Platonic realism

According to Platonic realism, universals exist in a "realm" (often so called) that is separate from space and time; one might say that universals have a sort of ghostly or heavenly mode of existence, but, at least in more modern versions of Platonism, such a description is probably more misleading than helpful. It will make the theory seem less mysterious if we say, instead, that it is meaningless (or a category mistake) to apply the categories of space and time to universals. In any event, we never see or otherwise come into sensory contact with Platonic universals, and they definitely do not exist at any distance, in either space or time, from our bodies. Obviously they do not exist in the way that ordinary physical objects exist. Nonetheless these universals do, according to Plato and other Platonic realists, exist.

Plato's theory of universals is also called 'Platonism', or 'Platonic realism', or just 'realism' for short. This sort of realism must not be confused with other doctrines called 'realism' in philosophy or in other fields. The word 'realism' is extremely ambiguous; it has a dozens of different senses in philosophy and also outside of philosophy. 'Platonic realism' is probably most precise.

The forms

These sorts of universals are called, after Plato, forms or ideas, but Plato's universals certainly are not ideas in the mind. They are not mental entities at all, unless, as on some theories, they are ideas in God's mind. Due to the potential confusion, 'form', 'Platonic form', or simply 'universal' are terms more usually used by philosophers. (See The Forms.)

To flesh out Plato's view, we might say, first, that the forms are archetypes, meaning original models, of which particular objects, properties, and relations are copies. So this apple is a copy of the form of applehood, this particular redness here is a copy of the form of redness, and so forth. Particulars are then supposed to be "copies" of the forms--whatever "copy" is supposed to mean here. That, anyway, is one way that, on Plato's view, the forms might be related to particular instances of objects and properties and so on. Another way they might be related, for Plato, is that particulars are said to participate in the forms, and the forms are said to inhere in the particulars. This talk of "participation" and "inherence" is admittedly rather mysterious. What does it mean to say this apple participates in applehood? What does it mean to say applehood inheres in this apple? We do not get very enlightening answers from Plato, as we will see shortly.

To further flesh out Platonic realism, it is useful to consider how the theory satisfies the three constraints on theories of universals listed on problem of universals.

Problems such what participation is, and how we can have any concept of the forms, would appear to be very difficult. Nonetheless, realism in fact does still have its strong defenders.