Plato

B

Middle Dialogues

Whereas the early dialogues seem to depict Socrates as Plato knew him, the middle and late dialogues seem to represent Plato’s own philosophical development, even though a character named Socrates often leads the discussions. The middle period is considered the great constructive phase of Plato’s thought, distinguished by the central role of the theory of forms (see below). Exemplars of this stage are the Symposium, a discussion of love as motivating the search for the forms; Timaeus, which uses the forms as models in reconstructing the principles of the cosmos; The Republic, Plato’s longest, most complex, and ambitious work, on the nature of justice in the soul and in the state; and, arguably, as stated above, the Phaedo.

C

Late Dialogues

The works of the later period seem no longer to treat the theory of forms as a central plank in constructing the true philosophy. Instead they criticize this theory and discuss a number of other philosophical problems, often abstractly. These works include Theaetetus, which seeks a definition of knowledge and exemplifies the way discussion can help develop ideas; Parmenides (which begins with a critical evaluation of the theory of forms); The Sophist, which discusses being and not-being in order to distinguish the sophist from the philosopher; The Statesman, which analyses the role of the true statesman in the ideal city; Philebus, on the relationship between pleasure and the good; and The Laws, Plato’s unfinished last work, which proposes the laws needed to mediate between human irrationality and rational knowledge.

IV

Theory of Forms

At the heart of Plato’s constructive philosophy is his theory of forms, or ideas. This notion underpins his view of knowledge, his ethical theory, his psychology, his concept of the state, and his perspective on art.

A

Theory of Knowledge

Plato’s theory of forms and his theory of knowledge are interrelated. Influenced by Socrates, Plato sought to understand the nature of the genuine knowledge that his teacher had professed to lack. He held that such knowledge must be correlated with the nature of the real: as the fully real is fixed, permanent, and unchanging, so must knowledge be certain and immune to revision or correction. Only such knowledge can be teachable. In his middle period he identified knowledge with knowledge of certain objects that are most truly real in this sense, and which underlie the mutable and misleading world of appearances. These are the forms.

It follows that sense experience and perception are worthless as routes to knowledge; they inform us only of the appearances or “phenomena”, not of the real essences. The sole route to knowledge is reason, the faculty of perceiving intelligible objects as contrasted with the senses, which perceive physical objects. The famous images of Sun, line, and cave that Plato uses in The Republic express this understanding of knowledge. The image of the Sun suggests that as the Sun is the condition for the perceptibility of physical objects, so the form of the Good is the condition of the intelligibility of the forms; in other words, he implies that a notion of value is pervasive and fundamental to reality.

B

Nature of Forms

The theory of forms applies centrally to moral and ethical notions. Nonetheless, the best way to begin to understand the forms is to compare them with mathematical entities, exactly as Plato does in the image of the line in The Republic. A circle, for instance, is a plane figure composed of a series of points, all of which are equidistant from a given point, yet none of which occupy any space themselves. No one has ever seen an ideal circle; one only ever sees approximations of the mathematical version, since all physical circles do occupy some space. An ideal circle would be perfect, timeless, and the model for the circularity of all ordinary circles. In the same way, the forms—such as Beauty and Good—are perfect, timeless entities. Ordinary physical objects resemble (“participate in”) the forms, and thereby gain whatever reality they have. In this sense, the postulation of forms belongs both to epistemology (the study of knowledge) and ontology (the study of what there is).

Most of Plato’s arguments for and about the existence of forms move from the instability and relative qualities of physical objects to the claim that some stable objects must exist as benchmarks for those that are comparative and changing. Occasionally, as in Book X of The Republic, he seems to suggest that every universal term (such as “bed” or “table”) must correspond to a form. However, this suggestion is out of place in the bulk of the discussion of forms.