The most famous of Socrates's pupils was an aristocratic young man named Plato. After the death of Socrates, Plato carried on much of his former teacher's work and eventually founded his own school, the Academy, in 385. The Academy would become in its time the most famous school in the classical world, and its most famous pupil was Aristotle.

   We know much about Plato's teachings, because he wrote dialogues between Socrates and others that would explore philosophical issues. These dialogues would be used in his school as starting points for discussion; these discussions and Plato's final word on the dialogues have all been lost to us. The Platonic dialogues consist of Socrates asking questions of another and proving, through these questions, that the other person has the wrong idea on the subject. Initially, Plato seems to have carried on the philosophy of Socrates, concentrating on the dialectical examination of basic ethical issues: what is friendship? what is virtue? can virtue be taught? In these early Platonic dialogues, Socrates questions another person and proves, through these questions, that the other person has the wrong idea on the subject. These dialogues never answer the questions they begin with.

   However, Plato later began to develop his own philosophy and the Socrates of the later dialogues does more teaching than he does questioning. The fundamental aspect of Plato's thought is the theory of "ideas" or "forms." Plato, like so many other Greek philosphers, was stymied by the question of change in the physical world. Heraclitus had said that there is nothing certain or stable except the fact that things change, and Parmenides and the Eleatic philosophers claimed that all change, motion, and time was an illusion. Where was the truth? How can these two opposite positions be reconciled? Plato ingeniously combined the two; a discussion of Plato's theory of forms is below.

   The most famous of Plato's dialogues is an immense dialogue called The Republic , and, next to his account of Socrates's trial, The Apology , The Republic is one of the single most influential works in Western philosophy. Essentially, it deals with the central problem of how to live a good life; this inquiry is shaped into the parallel questions (a) what is justice in the State, or what would an ideal State be like, and (b) what is a just individual? Naturally these questions also encompass many others, such as how the citizens of a state should be educated, what kinds of arts should be encouraged, what form its government should take, who should do the governing and for what rewards, what is the nature of the soul, and finally what (if any) divine sanctions and afterlife should be thought to exist. The dialogue, then, covers just about every aspect of Plato's thought. There are several central aspects to the dialogue that sum up Platonic thought extremely well: a.) what the nature of justice is; b.) the nature of an ideal republic; and c.) the allegory of the cave and the divided line, both of which explain Plato's theory of forms.   The Nature of Justice. The question which opens this immense dialogue is: what is justice? Several inadequate definitions are put forward, but the most emphatically presented definition is given by a young Sophist, Thrasymachus. He defines justice as whatever the strongest decide it is, and that the strong decide that whatever is in their best interest is just (review again the Athenian position in Melian Debate). Socrates dismisses this argument by proving that the strong rarely figure out what is in their best interest, and this can't be just since justice is a good thing.
   The Analogy of the Ideal Republic. After Thrasymachus leaves in a royal huff, Socrates starts the question all over again. If one could decide what a just state is like, one could use that as an analogy for a just person. Plato then embarks on a long exposition about how a state might embody the four great virtues: courage, wisdom, temperance, and justice. The remainder of the dialogue is a long exposition of what justice in a state is; this section is considered one of the first major, systematic expositions of abstract political theory . This type of thinking, that is, speculating about an ideal state or republic, is called "utopian" thinking (utopia is a Greek word which means "no-place").
   Plato (speaking through Socrates) divides human beings up based on their innate intelligence, strength, and courage. Those who are not overly bright, or strong, or brave, are suited to various productive professions: farming, smithing, building, etc. Those who are somewhat bright, strong, and especially courageous are suited to defensive and policing professions. Those who are extraordinarily intelligent, virtuous, and brave, are suited to run the state itself; that is, Plato's ideal state is anaristocracy, a Greek word which means "rule by the best." The lower end of human society, which, as far as Plato is concerned, consists of an overwhelming majority of people in a state, he calls the "producers," since they are most suited for productive work. The middle section of society, a smaller but still large number of people, make up the army and the police and are called "Auxiliaries." The best and the brightest, a very small and rarefied group, are those who are in complete control of the state permanently; Plato calls these people "Guardians." In the ideal state, "courage" characterizes the Auxiliaries; "wisdom" displays itself in the lives and government of the Guardians. A state may be said to have "temperance" if the Auxiliaries obey the Guardians in all things and the Producers obey the Auxiliaries and Guardians in all things. A state may be said to be intemperate if any of the lower groups do not obey one of the higher groups. A state may be said to be just if the Auxiliaries do not simply obey the Guardians, but enjoy doing so, that is, they don't grumble about the authority being exercised over them; a just state would require that the Producers not only obey the Auxiliaries and Guardians, but that they do so willingly.
   When the analogy is extended to the individual human being, Plato identifies the intellect with the Guardians, the spirit or emotions with the Auxiliaries, and the bodily appetites with the Producers. Therefore, an individual is courageous if his or her spirit is courageous and an individual is wise if his or her intellect is wise. Temperance occurs when the emotions are ruled over by the intellect, and the bodily appetites are ruled over by the emotions and especially the intellect. An individual may be said to be just when the bodily appetites and emotions are not only ruled over by the intellect, but do so willingly and without coercion.

   Does this arrangement satisfy you? Is this a fair division of the human soul? Is this a fair division of society? Before you even read Plato's critique of democracy, what do you think he would say about it? Would a democratic state be courageous, wise, temperate, and just based on the system Plato sets up here? What would Plato think of American democracy, which is based on elected representatives? What is the "democratic individual" and how does this creature come about? What happens to individuals in a democracy?   The Allegory of the Cave and the Divided Line: Far and away the most influential passage in Western philosophy ever written is Plato's discussion of the prisoners of the cave and his abstract presentation of the divided line. For Plato, human beings live in a world of visible and intelligible things. The visible world is what surrounds us: what we see, what we hear, what we experience; this visible world is a world of change and uncertainty. The intelligible world is made up of the unchanging products of human reason: anything arising from reason alone, such as abstract definitions or mathematics, makes up this intelligible world, which is the world of reality. The intelligible world contains the eternal "Forms" (in Greek, idea ) of things; the visible world is the imperfect and changing manifestation in this world of these unchanging forms. For example, the "Form" or "Idea" of a horse is intelligible, abstract, and applies to all horses; this Form never changes, even though horses vary wildly among themselves—the Form of a horse would never change even if every horse in the world were to vanish. An individual horse is a physical, changing object that can easily cease to be a horse (if, for instance, it's dropped out of a fifty story building); the Form of a horse, or "horseness," never changes. As a physical object, a horse only makes sense in that it can be referred to the "Form" or "Idea" of horseness.
   Plato imagines these two worlds, the sensible world and the intelligible world, as existing on a line that can be divided in the middle: the lower part of the line consists of the visible world and the upper part of the line makes up the intelligible world. Each half of the line relates to a certain type of knowledge: of the visible world, we can only have opinion (in Greek: doxa); of the intelligible world we achieve "knowledge" (in Greek, epistemŽ). Each of these divisions can also be divided in two. The visible or changing world can be divided into a lower region, "illusion," which is made up of shadows, reflections, paintings, poetry, etc., and an upper region, "belief," which refers to any kind of knowledge of things that change, such as individual horses. "Belief" may be true some or most of the time but occasionally is wrong (since things in the visible world change); belief is practical and may serve as a relatively reliable guide to life but doesn't really involve thinking things out to the point of certainty. The upper region can be divided into, on the lower end, "reason," which is knowledge of things like mathematics but which require that some postulates be accepted without question, and "intelligence," which is the knowledge of the highest and most abstract categories of things, an understanding of the ultimate good.