It is often said that Plato has a 'Theory' of Forms and even that it dominates his entire work. In fact
Forms appear rarely and are always discussed untechnically; they answer to a variety of needs which are
never systematically brought together; and they are prominent only in the early to middle dialogues,
which progress towards an ever more grandiose and all-embracing conception of them. They are objects
of pure thinking, and thus separate from our experience; yet in a strange fashion they motivate us to
grasp them in a way that lifts us out of our everyday individual concerns. In the Phaedo, Symposium,
Republic, and Phaedrus Plato gives famous poetic expression to the thought that the reasoning part of us
is drawn to the Forms in a way that is both rigorously argued and a kind of mystical communion; and
that by comparison the rest of our life is worthless and a mere distraction.
If we ask 'What are Forms?' we find a variety of answers. They are objects of knowledge (and hence, as
we have seen, of reasoning). A central thought is that the Form F is what has the quality F essentially;
this is the heart of the most extended argument for Forms, which recurs in different guises (Phaedo 74-6,
Republic 475-80, 523-5). When we say of things in our experience that they are just, or equal, we can
equally well ascribe to them the opposite of that quality, for a variety of reasons, such as applying a
different standard. This possibility, it is claimed, shows that in our experience there are no beautiful
things that are not also ugly, no just actions that are not also unjust. So (unless we are to infer, which
Plato never does, that the use of these terms is always relative to some standard) they cannot be applied
without the possibility of the opposite also applying within our experience, but only to the Form, the
Form of F which is essentially F and never not-F, and which the F things and actions in our experience
'partake of' (in so far as we can correctly call them F) but also 'fall short of (in so far as we can also say
of them that they are not F). This argument applies only to terms that have opposites, and so, while it
will serve for terms that exercise Plato in the early dialogues, such as just, beautiful, and equal, it will
not show that there are Forms of Square or Triangle, or of substances such as men or artefacts such as
tables. It is disputed whether Plato ever seriously wanted there to be Forms for these cases, and, if so,
what his motivation could have been. In Republic 10 we find the notorious Forms of Bed and Table, but
at Parmenides 130 b-d young Socrates is made to say that he is unsure whether there are Forms even for
substance terms. Plato never gets to the root of another problem, either: why, given the argument, he
concludes that they are Forms for the good opposites only and not for ugly, unjust, and so on. Mostly he
ignores these, though in one passage (Theaetetus 176-7) he allows that there are evil and negative
Forms, which the evil and ignorant person comes to resemble.
The role of Forms as essential bearers of qualities which in our experience always turn up contaminated
by the possible application of their opposites explains some of the uses to which they are put: for
example, in the Phaedo (100 ff.) they figure as preferred explanations for why things in our experience
have the qualities they do. But some of the Forms' roles are less clearly motivated; sometimes, for
example, they are taken to be stable and unchanging objects as opposed to the changing objects in our
experience; occasionally we find Forms to be models for artefacts. Most centrally, Forms are contrasted
with the supposedly defective way in which particular objects have certain qualities: but sometimes it is
types of object or action that provide the contrast. However, sometimes they are contrasted with
particular objects themselves, whose supposed fault is that they change, or even that there are many of
them and not one. Because of the dialogue form, Plato never has to say which of his arguments for
Forms is fundamental, and what their relations are; and because the arguments and contexts of