Socrates adamantly denies that he can identify a single state at the time of this dialogue that might prove fruitful for the growth of a philosopher-ruler; he says that, because of his environment (the society in which he finds himself), the naturally good, budding philosopher becomes warped. But Socrates anticipates the resultant clamor from a public whom he has accused of being corrupt, and he attempts to placate that public by insisting that a philosopher-ruler would still be the ideal ruler for the ideal state.
The problem, Socrates says, for our producing a philosopher-ruler may lie in the material with which we have to work. We agree that such a ruler must be intelligent, a “quick study,” ambitious in things of the mind, diligent. At the same time, the potential ruler must be disciplined, temperate, reliable. But intelligent people may be intemperate and unreliable, and they may lack courage. Reliable people, conversely, are often indolent and bored when facing intellectual tasks; such people are often ignorant and may be stupid. Citizens who possess all the qualities required in a philosopher-ruler will be in a distinct minority.
Thus it is that candidates for the capacity as ruler will have to be more thoroughly educated than we had thought; they will have to pursue a more rigorous intellectual training so that they can attain knowledge of the real.
Glaucon asks Socrates if he means that the potential rulers are to have knowledge of the Forms. Socrates replies that the rulers must possess knowledge of Goodness, for logically that is the sole way a man may recognize the goodness of, say, Justice and Beauty.
Logically, Socrates must at this juncture entertain a definition of Goodness, but we cannot accept the premise that “knowledge of the Good is Goodness”; that constitutes an invalid argument (a false tautology). And some people offer other invalid arguments for Goodness, as we may observe.
Socrates then says that he will not precisely define Goodness, but that he can elucidate the argument by arguing another analogy. Socrates’ analogy involves a comparison between sight and knowledge. In order for men to see, men must be given visible objects to perceive, and men must be given light in order to perceive the objects. The source of this light is the sun. Analogically, in order for men to know anything, men must be able to think, and they must be provided objects of knowledge (the Forms). Visible objects, then, have to be in the light; objects of knowledge have to be true. Light comes from the sun; truth comes from Goodness. (This analogy has come to be known as the Analogy of the Sun.)
