With all of that mental furniture about Zeno in place, it will be much easier to tackle the Parmenides. We will nevertheless do it in stages, because it is one of the deepest of the dialogues.
I think I'm going to do this as a direct encounter with the dialogue first, so that it's just you and me reading it and discussing it together. After that, we can look at other accounts of it. For now, you don't need anything that you won't find either here or in the dialogue.
The dialogue begins many years after the discussion between Socrates and Zeno and Parmenides. Several travelers come to Athens to hear the account of the discussion they had -- not from anyone who was there, because it was too long ago, but from a man who knew a man who was there. This underlines the importance of oral culture to this period of Ancient Greece, which was discussed in the prefaces. They clearly have confidence that the recitation will be accurate, and it probably more or less is; in Iraq, where oral culture remains strong among the tribes, the witness accounts of a bargain is considered more accurate than a written version of the agreement. The honor of the men, and their oath that they are speaking accurately and honestly, is thought a better guarantee than a paper that might be altered by anyone.
He told us that Pythodorus had described to him the appearance of Parmenides and Zeno; they came to Athens, as he said, at the great Panathenaea; the former was, at the time of his visit, about 65 years old, very white with age, but well favoured. Zeno was nearly 40 years of age, tall and fair to look upon; in the days of his youth he was reported to have been beloved by Parmenides. He said that they lodged with Pythodorus in the Ceramicus, outside the wall, whither Socrates, then a very young man, came to see them, and many others with him; they wanted to hear the writings of Zeno, which had been brought to Athens for the first time on the occasion of their visit. These Zeno himself read to them in the absence of Parmenides, and had very nearly finished when Pythodorus entered, and with him Parmenides and Aristoteles who was afterwards one of the Thirty, and heard the little that remained of the dialogue. Pythodorus had heard Zeno repeat them before.
Plato gives us a chance to get comfortable with these people, to know them not just as advocates for ideas but as human beings who lived and breathed, loved and fought. The mention of 'the Thirty' reminds us also that they sometimes killed each other, and turned to tyranny and violence as well as philosophy. Zeno will portray his ideas as a youthful defense of his master, Parmenides, who is also his lover.
If you've read the three preface pieces below, you are better positioned to follow what Socrates and Zeno discuss as an opening.
Socrates requested that the first thesis of the first argument might be read over again, and this having been done, he said: What is your meaning, Zeno? Do you maintain that if being is many, it must be both like and unlike, and that this is impossible, for neither can the like be unlike, nor the unlike like-is that your position?
Just so, said Zeno.
And if the unlike cannot be like, or the like unlike, then according to you, being could not be many; for this would involve an impossibility. In all that you say have you any other purpose except to disprove the being of the many? and is not each division of your treatise intended to furnish a separate proof of this, there being in all as many proofs of the not-being of the many as you have composed arguments? Is that your meaning, or have I misunderstood you?
No, said Zeno; you have correctly understood my general purpose.
Consider Aristotle's discussion of a thing moving from being white to being non-white (e.g., a man obtaining a suntan). If the man is one, i.e. the same man, then he can't really move to being unlike himself. The man who has beet red skin is unlike the man who had white skin. Thus, if he is both like himself (the same man) and unlike himself (the 'two' men have differently colored skin). The man cannot be both 'like' and 'unlike' himself; this is because 'the like' and 'the unlike' are contradictions. Thus there can only be one man, not two; and he cannot change from the one to the other, because he would have to pass through stages of being unlike himself.
A similar argument is at work here. There cannot be many things, like there cannot be 'two' men, because if there were they would have to be like and unlike each other. We don't have Zeno's account of why this is. A plausible reconstruction: because to recognize two birds as 'two birds,' we would have to say that they are like each other to say both are birds. Yet they must also be unlike in order to be two different birds. Thus they must be like and unlike at the same time, which is a contradiction.
Socrates is going to propose a novel attack on this idea of contradictions arising from the discussion of things moving or being many. This either becomes the Platonic idea of Forms (if Plato is accurately recounting Socrates' discussion) or is that idea (if Plato is reading it back into the discussion).
[T]ell me, Zeno, do you not further think that there is an idea of likeness in itself, and another idea of unlikeness, which is the opposite of likeness, and that in these two, you and I and all other things to which we apply the term many, participate-things which participate in likeness become in that degree and manner like; and so far as they participate in unlikeness become in that degree unlike, or both like and unlike in the degree in which they participate in both? And may not all things partake of both opposites, and be both like and unlike, by reason of this participation?-Where is the wonder? Now if a person could prove the absolute like to become unlike, or the absolute unlike to become like, that, in my opinion, would indeed be a wonder; but there is nothing extraordinary, Zeno, in showing that the things which only partake of likeness and unlikeness experience both. Nor, again, if a person were to show that all is one by partaking of one, and at the same time many by partaking of many, would that be very astonishing. But if he were to show me that the absolute one was many, or the absolute many one, I should be truly amazed.
"An idea of X in itself," and all similar formulations, are going to end up equivalent to "there exists a Form of X." I shall indicate that by capitalizing the first letter when talking about the Form of something like Likeness rather than, say, an instance of likeness. What Socrates is saying is that the likeness of the birds isn't really contradictory to their unlikeness; rather, Likeness and Unlikeness are contradictories. But the birds merely participate in Likeness to some degree, and also in Unlikeness to some degree. Thus, there is no logical contradiction implied, because the birds aren't contraries; and they don't fully participate in either of the Forms.
Plato intends to argue that the Forms are metaphysically real, indeed more real than you or I. You don't have to go that far to see value in this argument. For example, treat them as merely psychological facts rather than metaphysical entities. Let me draw an example.
Consider three houses, two of which were built on the same pattern by the same builder, but one of which is painted red and the other is painted green. The third house is different in pattern and builder from the other two, but is also painted red like the first house. Now the red houses are alike in being red, and unlike the green house. But the two houses that are on the same pattern are alike in design (and perhaps in purpose -- more on that shortly), but unlike in color.
Now our idea (not in this paragraph used to mean 'Form') that the two houses are like in color really does exist in our mind. When we are thinking about what makes them alike, we note this feature of color. But the color is manufactured by our minds, out of evidence collected by our eyes as interpreted by our brains. You might think that their physical layout is a more pragmatic fact, but 'design' is an intelligible layout that was first in the mind of the builder. If it is in the houses now, it is because he put it there. Thus, their likeness in all cases is a product of mind; and our ability to say that they are alike is itself the product of our idea of what would make two things alike. By the same token, our idea that they are different comes from our notion of what it would mean for two things to differ. Thus, the ideas of likeness and unlikeness do exist separately from the houses; they exist in our minds, while the houses are in the world.
One possibility is that Plato may be mistaking physical/psychological differences for metaphysical differences. You'll have to sort out what you believe about the metaphysical claims as we read this dialogue. But to complicate that process a bit further, let's talk about whether or not there really are three things here, or only two.
Back in the first preface, I gave a plausible account of what it means for there to be different things:
It seems like there are obviously many things, though. You can look around you and see what appear to be many different things. In my vision right now are this computer, a coffee cup with a skull and crossbones on it, and a Gerber Applegate-Fairbairn combat knife. It seems like these are several separate things, not just because they don't appear to be touching, but because my mind knows what each of these artifacts is for and it's not the same thing. Since each artifact has a distinct purpose, it must have a distinct reason for having come into being; and thus, since each thing was made at a different time for a different reason, it follows that they must be different things.
Say the two houses that are alike in design were built by the same builder, at the same time, and for the same purpose: to fulfill a contract to a purchaser who wanted to put his family in the two structures. If that is true, then they came into being in the same way at the same time and for the same purpose. In that way, they are plausibly one thing: one work, which was done for one purpose. Indeed, the builder had one purpose -- to make money -- and the purchaser also had one purpose -- to house his family.
Yet they are also plausibly two things: two houses, which are unlike in being physically separate and also in having been painted different colors.
I think the intuitive thing most people would say is that the 'twoness' of them overrides the 'oneness' of the purpose; of the design; the unity of their coming-to-be; the oneness of the work of their author. And yet we might even talk about them as being one thing if we were giving an account of the development of the neighborhood: "The Morgan estate was built in 1943 by Bob Roy, with stone he brought up from the White River, timber milled on the property, and roof tiles they baked out of the mud." In that way, what we would intuitively describe as two (houses) becomes one (estate), and is sensibly treated as a single entity.
So which is it? A single thing? Two things? Is the difference metaphysical or psychological? Which one is the 'real' thing, and which one(s) are just ways of speaking or thinking about the things that really exist?
