Plato invented his forms, I suggested in #2, by cleaning up the gods; and “cleaning up” deserves slightly more discussion (actually, a lot more; but I’ll keep it short). First, they must be made self-consistent: instead of a mass of impulses and projects, a god must become a pure unity. It therefore cannot be as multifarious (or as interesting) as Zeus or Hera, but must be identified with a single basic property or character, from which it never departs: it becomes an unchanging “form” (εἴδος). Death, of course, would be a change; so the form, like a god, exists forever. Since a form never changes, what it causes is always the same: a form always affects human affairs in the same way. Not only is it eternal itself, but its eternal causal activity can sustain us forever.
We now have a much more positive vision of the afterlife than Homer’s, but one bought at a price: the need for immortality has led us to postulate another realm, one where things are perfectly what they are and so never change. (There are, to be sure, other motives for, and problems with, the theory of forms; see H. F. Cherniss’ famous “The Philosophical Economy of the Theory of Ideas” for a starter on this.)
But even cleaned-up gods must be kept away from our minds; if we are merely the forms’ playthings, as we were the gods’, the whole idea of ethics is undone. This runs Plato against a problem, for he never sorted out the nature of the human mind. Soul not only exists, for example, on both the level of the forms and that of experienced things, but somehow rises and falls between them—a “fact” which for Plato remains inexplicable, an “ordinance of necessity” (Phaedrus 248c).
In particular, as I have argued elsewhere (Metaphysics and Oppression, Appendix 1), Plato never assigns stable boundaries to the mind: things perceived at a distance, such as a beautiful body, can enter into the soul (in the Palinode of the Phaedrus, as a flow of particles) and affect its inner core. If bodies can do this, can’t forms do so as well?
The problem can be solved by locating the forms, not merely outside our minds, but outside our world altogether. Easy enough to do, once you have placed them outside of time. Time thus becomes the defining property of the human and natural worlds, and its absence helps define the world of the forms.
A form resembles itself in all aspects: it is self-identical. So the predicational philosophy practiced by Thales (at least as Aristotle reads him) is restricted to the higher, formal level of Plato’s bifurcated cosmos. The variability and passions of the gods now inhabit the human world, where variability and passion have always existed, and where they now exist exclusively. And so we find ourselves in the wonderful, variegated world of the Platonic dialogues, from which no human emotion is excluded.
The characters there are memorable. You have the hilariously stupid Hippias, who thinks the form of beauty—the one thing, supremely beautiful itself, that makes all other beautiful things beautiful—might be gold. There is Thrasymachos, whose energetic cynicism and vigorous argumentation are, in the end, terrifying. There is sincere Phaedrus, whose enthusiasm for learning is as touching as his judgment about whom to learn from is risible. There is gorgeous Charmides, who—right in the middle of his eponymous dialogue—sets off a homosexual group grope.
Reading Plato in Greek is actually scary, because eventually you must admit that you are putty in his hands. If he wants you to fall in love with someone (Socrates), you will fall; if to hate someone (Anytus, Meletus), you will hate them; if to pity someone (Cephalus), you will pity them. If Plato wants you to laugh, you obediently laugh; if to cry, you cry. If he wants you to pick the book up and dance around the room with it, you will do that too.
But for all his genius, there is a flaw in our author. Socrates never defined a single form, because he didn’t think we could have such knowledge until we died; such was the main promise of the Socratic afterlife. And Plato, in his later writings, doesn’t really revoke this: when he turns from presenting Socratic aporiai, concluding bafflements, to his own “positive” ideas, the emphasis turns as well, from attempting to define single forms to more general discussions of their common status. No individual form is ever, then, defined by Plato. It can’t be; for while the forms themselves are pure and unchanging, we, our language, and the things around us are not. The best we can do, according to the Timaeus, is use a “bastard discourse” (λογισμός νὀθος, Timaeus 52b; cf. 29b-d) to treat these “likenesses” (εἰκόνα, 29c).
So there are two kinds of philosophy in Plato: philosophy among the forms, which deals in realities and attains truth—and which we are incapable of; and philosophy as we practice it, which deals in things similar to the forms and achieves likelihoods.
One seeming exception: the definition of justice in the Republic,which is as clear as can be: justice consists in each part of the soul or state doing its proper job. Plato never actually says, in the Republic, that he is discussing the form of the state and so of justice; but it’s hard to say what else it could be.
But there is something off about this definition: etwas stimmt nicht, as the Germans would say. Plato keys his treatment to two kinds of justice, justice in the state and in the individual. But rather than present these two cases separately, as Homer might, and then wrestle their commonality out of the presentations, Socrates stipulates that justice is the same in both cases. His warrant for this is that we say (φάμεν) that justice exists both in the individual and in the state; that we (Greeks) might speak ambiguously here is summarily excluded. That certain features apply to both forms of justice is therefore not wrested from the facts, but presupposed. The presupposition becomes a premise for the investigation, and argument suddenly replaces simile.
So the “bastard” discourse is abandoned—by simple decree. From first to last, Plato’s bastardly presentations of human inquiry—with all their humor, sorrow, fear, and desire—are tragic depictions of a group of people who cannot have what they most need—knowledge of the meanings of moral terms.