In his masterpiece dialogue, The Republic, Plato presents Socrates, speaking in the first person, retelling the course of a discussion on the nature of "justice." The main persons who provoke the discussion in the dialogue are Glaucon and Adiemantus, Plato's real life brothers. Socrates is challenged to defend his belief that the virtuous life -or as it is put in the dialogue "the life of the just man"- is the greatest in happiness. To make sure that it is really justice, and not merely the appearance of justice which leads to happiness, Socrates is to imagine a competition between the perfectly just man who shall appear to others (because of their ignorance) as supremely "unjust" versus the perfectly unjust man who is absolutely ruthless, observing no moral constraints in attaining what he wants, and moreover who possess a magical ability never to "get caught" and always appear to others as supremely "just."
Naturally we must first determine what "justice" is. Socrates' strategy is to analogize the human soul to the Greek city state (polis in Greek, which gets mistranslated "republic"), for the polis is the soul of its citizens "writ large." If we can discern where justice is found in the polis, we can then, in the analogy, see where it is found also in the individual human life. This leads Socrates to develop a model of an ideal just polis.
The view of the social-political whole which Plato gives here strikes most contemporary Western readers as "authoritarian" and neglectful of those "individual human rights" which form the philosophical basis of the democratic conception of political authority. Nevertheless, it should not be forgotten that the Greek polis is radically different from the contemporary nation state, and that Plato's avowed purpose is not to develop a realistic political system. Furthermore, perhaps somewhat ironically, the conception of "natural rights" which underlies contemporary justifications of democratic government, itself derives from a conception of what it is to be human that has at least one of its roots in Plato's philosophy.
For our purpose of understanding Plato's theory of knowledge (epistemology ) as presented in the Theory of Forms, it is not necessary to go into the details of Plato's ideal state; suffice it to say that as we would expect, the perfectly just state will be one ruled by the perfectly just ruler(s) . In the analogy to the soul, the ruler in the polis is the parallel to the "mind" (in Greek: nous) in the soul . As the eyeball is the organ with which the body is able to see , so the "mind" may be thought of as the "organ" with which the soul acquires knowledge. The perfectly just soul would then be a soul "ruled" by a mind which had perfect knowledge , complete wisdom. This use of "perfect" is intended to mean no possibility of error or mistake; the perfectly just ruler(s) will necessarily do what is right, for if an error was made, one could imagine a better ruler who didn't make that error. Obviously such an "ideal" may very well be humanly impossible, but, Socrates insists, it is still essential to have such a perfect ideal as a kind of "yardstick" against which to measure the degree of justice or injustice in actually existing states and people.
Socrates defends his conception against three "waves" of criticism directed by Glaucon and Adiemantus. The passage assigned begins with the third -and most devastating- of these waves, and this is the challenge to explain what least possible change in existing social-political institutions could bring about the realization of such an ideal, or at least move us as far as possible in that direction.
Socrates' answer is known as "the paradox of the philosopher king" and is stated dramatically at 473d: the way to bring about a just state is to have it ruled by philosophers, or what is commonly called "the Philosopher-King." This conclusion would naturally be felt as paradoxical by most of Socrates' listeners because philosophers were perceived as people with "their heads in the clouds" and consequently as manifestly unfitted for the realities of the political world. So now to defend his view, Socrates must finally tell us what he means by the ideal perfect "philosopher" and what sort of education would produce such a person.
We start with the root meaning of the word "philosophy"; the philosopher is the lover of wisdom. The philosopher is in pursuit of wisdom in all its forms, in love with learning. But people seek to learn many different kinds of things, are all of them philosophers? No, the philosopher is distinct from the others in that the philosopher wants to learn "the truth " as distinct from the false illusions (being sold by sophists in the marketplace). The learning of the philosopher is therefore the acquisition of true infallible knowledge , whereas others, those who follow the sophists. learn merely fallible "opinions" (in Greek: doxa)
So now the original question about justice, an ethical question, is transformed into an epistemological question: how do we distinguish true genuine knowledge (the real thing the philosopher seeks) from fallible opinions (the phony, "counterfeit" beliefs of the "lovers of opinions," the sophists). In answer Plato presents his most famous exposition of his "Theory of Forms" which extends all the way to 521b. Many crucial distinctions on which this theory is based appear in this discussion.
Click Here to find out about Plato's Theory of Forms