Platonic realism

Platonic realism is a metaphysical theory of universals, maintaining that universals have a mode of being that is independent of the experiential mode of being. It is founded largely on the works of Plato, partly inspired by the teachings of the Pythagoreans, though it is but one aspect of both those philosophies. A due appreciation of this position depends on understanding that the relation being independent of is not the same thing as the relation being exclusive of or the relation being separate from.

Platonic realism is also commonly referred to as simply Plato's theory of universals, just Platonism, or just realism. The latter two terms are problematic: the term realism has several meanings both in philosophical and in non-philosophical fields and the term Platonism refers to the entire philosophy of Plato and is often synonymous with Platonic idealism. The two terms are common shorthand, nevertheless, in certain contexts where they are understood.

The theory is expounded in The Republic and elsewhere, notably in the Phaedo, the Phaedrus, the Meno, and the Parmenides.

Universals
In Platonic realism, universals do not exist in the way that ordinary physical objects exist, but were originally thought to have a sort of ghostly or heavenly mode of existence. However, more modern versions of the theory do not apply such potentially misleading descriptions to universals. Instead, such versions maintain that it is meaningless (or a category mistake) to apply the categories of space and time to universals.

Regardless their description, Platonic realism holds that universals do exist in a broad, abstract sense, although not at any spatial or temporal distance from people's bodies. Thus, people cannot see or otherwise come into sensory contact with universals, but in order to conceive of universals, one must be able to conceive of these abstract forms. Most modern Platonists avoid the possible ambiguity by never claiming that universals exist, but "merely" that they are.

Theories of universals
Theories of universals, including Platonic realism, are challenged to satisfy the certain constraints on theories of universals.

Of those constraints, Platonic realism strongly satisfies one, in that it is a theory of what general terms refer to. Forms are ideal in supplying meaning to referents for general terms. That is, to understand terms such as applehood and redness, Platonic realism say that they refer to forms. Indeed, Platonism gets much of its plausibility because mentioning redness, for example, seems to be referring to something that is apart from space and time, but which has lots of specific instances.

Forms
One type of universal defined by Plato is the form or idea. Although some versions of Platonic realism regard Plato's forms as ideas in the mind of God, most take forms not to be mental entities at all, but rather archetypes (original models) of which particular objects, properties, and relations are copies. Due to the potential confusion of the term idea, philosophers usually use the terms form, Platonic form, or universal.

Particulars
In Platonic realism, forms are related to particulars (instances of objects and properties) in that a particular is regarded as a copy of its form. For example, a particular apple is said to be a copy of the form of Applehood and the apple's redness is a copy of the form of Redness. Participation is another relationship between forms and particulars. Particulars are said to participate in the forms, and the forms are said to inhere in the particulars.

According to Plato, there are some forms that are not instantiated at all, but, he contends, that does not imply that the forms could not be instantiated. Forms are capable of being instantiated by many different particulars, which would result in the form's having many copies, or inhering many particulars.

Criticism
Two main criticisms with Platonic realism relate to inherence and difficulty of creating concepts without sense-perception. Despite its criticisms, though, realism has strong defenders. Its popularity through the ages is cyclic.

Criticism of inherence
Critics claim that the terms instantiation and copy are not further defined and that participation and inherence are similarly mysterious and unenlightening. They question what it means to say that the form of applehood inheres a particular apple or that the apple is a copy of the form of applehood. To the critic, it seems that the forms, not being spatial, cannot have a shape, so it cannot mean be that the apple is the same shape as the form. Likewise, the critic claims it is unclear what it means to say that an apple participates in applehood.

Arguments refuting the inherence criticism, however, claim that a form of something spatial can lack a concrete (spatial) location and yet have in abstracto spatial qualities. An apple, then, can have the same shape as its form. Such arguments typically claim that the relationship between a particular and its form is very intelligible and easily grasped; that people unproblematically apply Platonic theory in everyday life; and that the inherence criticism is only created by the artificial demand to explain the normal understanding of inherence as if it were highly problematical. That is, the supporting argument claims that the criticism is with the mere illusion of a problem and thus could render suspect any philosophical concept.

Criticism of concepts without sense-perception
A criticism of forms relates to the origin of concepts without the benefit of sense-perception. For example, to think of redness in general, according to Plato, is to think of the form of redness. Critics, however, question how one can have the concept of a form existing in a special realm of the universe, apart from space and time, since such a concept cannot come from sense-perception. Although one can see an apple and its redness, the critic argues, those things merely participate in, or are copies of, the forms. Thus, they claim, to conceive of a particular apple and its redness is not to conceive of applehood or redness-in-general, so they question the source of the concept.

Plato's doctrine of recollection, however, addresses such criticism by saying that souls are born with the concepts of the forms, and just have to be reminded of those concepts from back before birth, when the souls were in close contact with the forms in the Platonic heaven. Plato is thus known as one of the very first rationalists, believing as he did that humans are born with a fund of a priori knowledge, to which they have access through a process of reason or intellection &mdash; a process that critics find to be rather mysterious.

A more modern response to the Platonic realism criticism of concepts without sense-perception is the claim that the universality of its qualities is an unavoidable given because one only experiences an object by means of general concepts. So, since the critic already grasps the relation between the abstract and the concrete, he is invited to stop thinking that it implies a contradiction. The response reconciles Platonism with empiricism by contending that an abstract (and thus not real) object is real and knowable by its instantiation. Since the critic has, after all, naturally understood the abstract, the response suggests merely to abandon prejudice and accept it.