The Phaedo and Republic

The parts of these two dialogues that we’re concerned with are about Plato’s theory of the Forms.

What are the Forms?

It’s not easy to figure just what Plato thinks the Forms are. But here's the rough idea: think about all of the red things out there. What do they all have in common? Being red. So the Form of redness is just whatever all red things have in common.

Similarly for any property: all good things have the Form of the Good; all rational things have the Form of rationality; and so on. Plato thinks that the Forms are the only explanation for these kinds of similarities (the similarity of all good things or red things or rational things or whatever).

Any particular object (a cat, for example) will have several Forms (the Form of feline-ness, the form of blackness, the form of being an animal, etc.). Which Forms the object has determine what the object is like (you can't be a black cat unless you've got the Form of blackness and feline-ness). You might say that the Forms control physical objects (though that’s probably a misleading way of speaking).

What are the Forms like?

Apparently, they’re abstract—that means they don’t exist in time or space (in the way numbers are abstract: it doesn’t make sense to ask where the number 2 is). Why does Plato think they're abstract? Plato will answer by asking you where you think, for example, the Form of redness is. It cannot be located in any particular red thing because if that red thing were destroyed, redness would still exist. Similarly, if all red things were destroyed, redness would still exist (though, obviously, nothing would be red).

The same sort of thinking also tells us that the Forms are eternal: they always have existed and they always will exist. All of this amounts to saying that the existence of the forms is independent of the existence of physical objects or people.

Plato thinks the forms are ordered in a hierarchy. Here's an example of a hierarchy:

The Forms at the top of Plato’s hierarchy are the most real Forms and the things at the bottom are the least real Forms. It’s not clear what Plato means by “more” and “less” real—maybe more or less awesome? Important: all Forms are ”more real“ than the objections of perception (the ordinary objects that we see and bump into). The highest Form for Plato, the one at the top, is the Form of the Good. This Form is really awesome.

How do we know about the Forms?

Since the Forms are abstract (not in time or space) we cannot know about them through perception (just like you can't hear, taste, touch, smell, or see the number 2). (Here's an interesting according to Plato: since the Forms are more real than physical objects, perception, which teaches us about physical objects, is not a good way of learning about what reality is really like.)

Plato thinks, for reasons we won’t go into, that our knowledge of the Forms is innate: we’re all born with it “built-in”. This isn’t a crazy view: it’s a pretty respectable view in linguistics that humans are born with innate knowledge of certain universal rules of grammar.

This doesn’t mean that everyone is an expert grammarian. Our innate knowledge of grammar is implicit—it’s something we know how to do without knowing how we do it (anyone who’s tried to learn the rules of English grammar knows that this is difficult, even if you can speak English perfectly well).

Our innate knowledge of the Forms is sort of like this. Everyone’s got it, but it takes a lot of training to make it explicit. (Math is about Forms, but we all know how hard it is to learn math.)

Cave Metaphor

To help explain his theory of Forms, Plato gives the Cave Metaphor. In it, we imagine a bunch of people living in a cave. They're tied up so that they can only see one wall. Behind them is a fire that casts their shadows on the wall. So all they can see is shadows. They think the shadows are what are real. They’re wrong the objects casting the shadows, and, especially, the fire itself are the real things.

Then we’re supposed to imagine that one day one of the people in the cave managed to untie himself and turn around. At first, he'd be blinded by the light of the fire. Then he’d get used to it and he’d learn that the shadows were’t real at all—they were just shadows. He might try to tell people what he had learned but they wouldn’t believe or understand him.

Finally, we imagine that this character one day manages to get out of the dark cave. He finally sees the sun! So much brighter (more real) than the fire! The sun is the most real, because everything else depends on it.

Here's what the different parts of the metaphor represent:

Plato is trying to teach us something he thinks is important: perception cannot teach us about what’s really real. Relying too heavily on perception is just going to make you ignorant and will even make it more difficult to learn the truth (remember how the guy in the cave was at first blinded by the light?).

Happiness

One more thing. Remember that Socrates thinks that happiness is always choosing the Good. Well, then you’re going to have a better chance at happiness if you know the Form of the Good! Quit looking at shadows and step out into the sun!