Republic Book 5

Just when you thought that Socrates had finished describing the details of his theoretical city and we were ready to move onto more interesting and more philosophical territory, Book 5 returns to add even more laws and prescriptions.  Socrates' companions demand that he elaborate on what he meant when he said that the guardians should possess wives and children in common (423e).  Most of the chapter is then consumed by a relatively boring discussion of the rules of guardian communism.  It's only towards the end, after he's described how it's not only possible and even natural to share wives and children, but also the best thing for the city, that Socrates gets back to more philosophical territory (473c2).  He argues that the single biggest thing we can do to actually bring this utopia into existence would be to put the philosophers in charge of the city.  We need a philosopher king (473c8).  While this conclusion is hardly surprising, the way he reaches it brings up some interesting material.

Socrates begins his incendiary discussion of group marriage by first establishing that women can be guardians too.  Oddly, however, this isn't because men and women are equal.  Socrates is clear that women are generally inferior in every respect (455d2).  Nevertheless, they have the same 'nature' as the men, which is to say that they are made of the same stuff, the same mix of metals.  In what appears to be an argument (perhaps by necessity) for some sort of relative scale of metallic purity, Socrates claims that women should have all the same jobs as the men.

Then there is no way of life concerned with the management of the city that belongs to a woman because she's a woman or to a man because he's a man, but the various natures are distributed in the same way in both creatures. Women share by nature in every way of life just as men do, but in all of them women are weaker than men. 
Certainly.
Then shall we assign all of them to men and none to women?
How can we?
We'll say, I suppose, that one woman is a doctor, another not, and that one is musical by nature, another not.
Of course.
And, therefore, won't one be athletic or warlike, while another is unwarlike and no lover of physical training? 
I suppose so.
Further, isn't one woman philosophical or a lover of wisdom, while another hates wisdom? And isn't one spirited and another spiritless? 
That too.
So one woman may have a guardian nature and another not, for wasn't it qualities of this sort that we looked for in the natures of the men we selected as guardians?
Certainly.
Therefore, men and women are by nature the same with respect to guarding the city, except to the extent that one is weaker and the other stronger. (455d5)

"Weaker" here seems to be synonymous with 'worse', not simply opposed to 'physically strong'.  So the hierarchy of women seems to be like a parallel double of the hierarchy already described for the men in the myth of the metals.  While an odd way to empower women by modern standards, this type of analogy is eminently Platonic.

Once we have female guardians, we need to know how they interact with the men and how children are reared.  At this point the discussion shades in a Nazi eugenic direction.  Basically Socrates wants all the guardians to think that they share wives and children completely in common, but to arrange a cunning mating system that allows the best guardian men to breed more often with the finest women.  The whole apparatus is to be disguised as some sort of ritual lottery so that no one catches on (460a5).  How we're supposed to deal with the fact that so many kids are mysteriously born with the same little dictator mustache is not discussed.  To make a long story short, the rules for sex, child rearing and war laid out in the whole long section (up through 471c) all aim at making sure the guardians operate as a single unit, like one big happy family, without any internal factions.  None of them are allowed to possess anything not shared with the whole family.  While this sort of structure is naturally a controversial social topic, there's not really anything philosophically interesting in Plato's treatment of it.  He's basically just reversing the initial analogy between a city and person.

As I observed at the outset, things only get interesting again when Socrates proposes that the first step in creating the just city is to put the philosopher's in charge (473c8).  Because at that point he has to first define what it is that distinguishes philosophy from other crafts.  The first distinguishing mark of the philosopher is that he is a lover of wisdom in its entirety, including all types of learning (475c7).  This, however, is not specific enough.  For the philosopher to truly separate himself from the dilettante, he has to rise beyond loving all particular kinds of learning and love wisdom itself, to love the unity of learning we call the pursuit of truth.  The philosopher is the one who wants to find the hidden unity of the Forms of learning and wisdom and beauty that lie beneath the various ways these manifest themselves in particular things.  

Since the beautiful is the opposite of the ugly, they are two.
Of course.
And since they are two, each is one?
I grant that also.
And the same account is true of the just and the unjust, the good and the bad, and all the forms. Each of them is itself one, but because they manifest themselves everywhere in association with actions, bodies, and one another, each of them appears to be many. (476)

Non-philosophers, like dreamers, see the many manifestations and take them for all of reality.  Philosophy begins by waking up to the fact that these many manifestations are mere images, mere likenesses, of single unitary Forms (476c-d).  Basically, if you don't believe in the theory of Forms, you can't be a philosopher.

The final pages of the chapter attempt to head off potential objection to this definition of philosophy.  Why can't one love wisdom and learning without believing in Plato's Forms?  Why isn't it okay to know and love a lot of different things?  In short, because the Forms are the only objects of true knowledge, while the myriad manifestations of the world are the objects of opinion.  To modern ears, this argument doesn't sound at all convincing; at best it seems just a restatement of the theory of Forms, and so wouldn't provide a non-circular ground to that theory.  But it may have sounded more plausible to Greek ears because of a peculiarity in the use of the verb "to be".

"Tell us, does the person who knows know something or nothing?" You answer for him.
He knows something.
Something that is or something that is not?
Something that is, for how could something that is not be known?  
Then we have an adequate grasp of this: No matter how many ways we examine it, what is completely is completely knowable and what is in no way is in every way unknowable? (476e6)

The translators note that the verb here could be construed in a number of ways.

Because of the ambiguity of the verb einai ("to be"), Socrates could be asking any or all of the following questions: (1) "Something that exists or something that does not exist?" (existential "is"); (2) "Something that is beautiful (say) or something that is not beautiful?" (predicative "is"); (3) "Something that is true or something that is not true?" (veridical "is"). (pg. 1103)

Plato will often slur together the good, the beautiful, the virtuous, the wise, and the true.  To this list we can add the knowable and 'that which is'.  If, as the translator's suggest, the very form 'to be' for the Greeks was identical to veridical predicability, then Socrates' attempt to justify his definition of philosophy by linking the Forms to knowledge takes on a new light.  Perhaps for the ancient Greeks, to know something is to know that something is X -- true, or beautiful, or existent ... real.  Hence what is (real) is knowable, and what is knowable is (real).  Likewise, you cannot know the unreal, that which is not, which is the domain of ignorance.  In between these two lies the realm of opinion, which deals with things that neither completely are nor are not (478d).  

Socrates goes on to use the fact that we know what is, we are ignorant of what is not, and we opine about things in between, in order to justify the idea that the Forms are acceptable object of knowledge as such.  The final step follows from the same 'veridical predicability' form of 'to be'.  If something is X, then it surely is not not-X at the same time.  But anything we encounter in the world of things could be truly described by either an adjective or its opposite so long as we're describing it relative to another thing.

I want to address a question to our friend who doesn't believe in the beautiful itself or any form of the beautiful itself that remains always the same in all respects but who does believe in the many beautiful things—the lover of sights who wouldn't allow anyone to say that the beautiful itself is one or that the just is one or any of the rest: "My dear fellow," we'll say, "of all the many beautiful things, is there one that will not also appear ugly? Or is there one of those just things that will not also appear unjust? Or one of those pious things that will not also appear impious?"
There isn't one, for it is necessary that they appear to be beautiful in a way and also to be ugly in a way, and the same with the other things you asked about.
What about the many doubles? Do they appear any the less halves than doubles?
Not one.
So, with the many bigs and smalls and lights and heavies, is any one of them any more what we say it is than its opposite?
No, each of them always participates in both opposites.
Is any one of the manys what we say it is, then, any more than it is not what he says it is?
No, they are like the ambiguities one is entertained with at dinner parties or like the children's riddle about the eunuch who threw something at a bat—the one about what he threw at it and what it was in, for they are ambiguous, and one cannot understand them as fixedly being or fixedly not being or as both or as neither.

Then do you know how to deal with them? Or can you find a more appropriate place to put them than intermediate between being and not being? (479)

We can never say that anything is truly beautiful or small or light or even half in itself.  These qualities all require a relative scale or more and less.  Something isn't beautiful, period, it's only more beautiful than, and also appears ugly when set beside something else.  Only the Form of Beauty is beautiful in itself.  Only Beauty is purely beautiful.  So only the Forms actually fit the Greek definition of 'being', where they are truly just X and not also simultaneously not-X.  In other words, the Forms are the only things that are, and hence the only things that can be known.  Everything else vacillates between being (X) and not being (X).  We can have opinions about those types of things, but not knowledge.  And since philosophy is all about gaining knowledge, the theory of Forms is the only philosophy.  QED.  Except for the fact that philosophy was supposed to be the love of wisdom, not the knowledge of it.  It seems like Socrates has pulled a fast one on us here.