Plato’s Theory of Forms

      The Theory of Forms says there is (i) the name or word, circle; (ii) the definition (logos); (iii) particular images or diagrams; (iv) knowledge of what a circle is; and (v) the abstract object or Form, both knowable and truly existent. The name is ambiguous, but its true meaning points to the Idea. (Cf. 7^th Letter, 342b.)

       Plato offers three chief arguments to defend his Theory of Forms (presented in several different dialogues):

·         Argument from Universals: If people use the same word (e.g. “justice”),  something must make it the same reality they are talking about, or they would be speaking private languages. But people constantly use the same word for different objects or events. Therefore there is a universal they refer to, the “one” over the many instances, the Form. This argument is rejected by relativists, but relativists must admit that there are universals, perhaps even moral universals (e.g. they must agree there is an idea of justice which is not the same as the idea of law, if they agree there can be just and unjust laws).

·         Argument from Imperfection: We conceive of perfect, abstract things such as the Equal, Circle, Square, etc. These concepts cannot derive from sense-perception, because we realize the particular things we perceive through the senses “fall short” of corresponding perfectly to them. But they are not fictions, like centaurs or Zeus. Therefore the Forms exist, i.e. abstract entities that have the characteristics we have in mind, and they are what we are thinking of, if thinking rationally. (Phaedo 74-76)

·         Argument from Knowledge. If scientific knowledge exists, that knowledge is expressed in universal, necessary truths, not merely particular, contingent truths based on generalizations from things we perceive. But it is clear that such knowledge exits—viz. the knowledge of mathematics, logic, ethics—and therefore their truths must refer to realities, i.e. the Forms. If there were no Forms, there could be no universal and necessary knowledge; there could only be general patterns of experience, which could always be mistaken or change.

Plato himself, and his later critics, including his student Aristotle, offered arguments against the Theory of Forms. (Cf. Parmenides126-135)

·         Reification: The Theory of Forms confuses concepts with objects. The Forms are thoughts or meanings in the mind; they aren’t beings, real things that exist. To think of them as things is to reify them, rather than recognize they are concepts.

·         Population: Do all kinds of Forms exist? Are there Forms of (1) natural things like Snow, Mud? (2) artifacts like Table, Spear? (3) comparatives like Great and Small? (4)  mathematical and logical concepts like Circle, Same? (5) moral concepts like Justice, Goodness? (A related issue is the question where a concept like Man belongs? Is man a strictly empirical concept, or does “man” imply an ideal, what man ought to be or become?) Platonists have disagreed about this issue—some claiming that only Forms of types (4) and (5) exist, others that they must all exist.

·         Self-reference or “Third Man”: If there are Forms for each kind of thing for which there are names, e.g. men, and therefore e.g. a Form of Man (the 2^nd Man), isn’t there a Form of the new group, composed of men + Man, i.e. another Form, a 3^rd Man? (This problem may be related to one below.)

·         Ambiguity: Whatever may be true about the Forms, it seems impossible to express it unambiguously. A term like “square” refers both to the physical world (to physical squares) and to the idea of the Square (which is ideal and non-physical), similarly, e.g. justice or terms like identity or difference. Doesn’t this make it impossible to express truths about the Forms in ordinary language?