In the Gorgias, Plato distinguishes between philosophy and rhetoric, characterizing Gorgias as an orator who entertains his audience with his eloquent words and who believes that it is unnecessary to learn the truth about actual matters when one has discovered the art of persuasion.

In his dialogue Protagoras, Plato credits him with having invented the role of the professional sophist or teacher of virtue.

Protagoras suggests that the ability and knowledge to make decisions and rule is distributed to all humans, not just a few. Books II-IV of The Republic assume that Protagoras' position is wrong.

For Pythagoras himself, we have no evidence that he was an active mathematician. We don't really even know if he discovered the "Pythagorean theorem." We do know that he thought number and proportions were important, perhaps merely symbolically, for understanding reality. He was a charismatic leader of a close knit group who apparently followed rules of association and his main teaching was about the soul and its place in the cosmic order.

In the Parmenides, Parmenides and Socrates argue about dialectic. In the Theaetetus, Socrates says that Parmenides alone among the wise denied that everything is change and motion.Plato's Parmenides consists in a critical examination of the theory of forms, a set of metaphysical and epistemological doctrines articulated and defended by the character Socrates in the dialogues of Plato's middle period.

Heracleitus of Ephesus (535-475BCE) was a philosopher before Socrates' time who said, roughly speaking, that all things are constantly changing: the only constant is change. Thus you are not the same from moment to moment. Everything is like a river, constantly flowing and changing. There is no stable being. We have nothing but fragments, and few at that, of Heraclitus' writing, so we can't really be sure what exactly he meant by what he said. We know more about what Plato and Aristotle called "Heracliteanism"

Book II of The Republic.

Glaucon and Adeimantus are not satisfied with Socrates' refutation of Thrasymachus' idea, they suggest that the real task is to say why one should choose justice EVEN IF one does not have the conventional rewards of justice. From this comes "Gyges ring": there's a magic ring that enables one to "get away with" injustice: a conceit, but is it implausible? Glaucon's challenge is now answered: justice is good for one's soul and one's soul just is one's self.

The culmination of the Philosopher's education will be knowledge of the Form of the Good.  The sun is meant to illustrate the power of the Form of the Good. The divided line shows the four stages of cognition which the guardians must go through on the way to acquiring knowledge of the Form of the Good.

The individual has the same three principles as those found in the State, because he is affected in the same manner. The three parts of the soul consist of Anger, Desire, and Passion. It is from the individual that these principles pass into the State. There is no other way for these principles to come into the State.

In Book II, the Principle of Specialization is introduced: each citizen does one job only, and that leads to the three different classes in the state, a ruler class, a permanent professional military class, and a producer class The Principle of Specialization rules out democracy: only the rulers know the Good. Good because of the uneven distribution of natural talents, and efficiency.

On his return from Sicily, Plato founded the Academy, a group of philosophers who met at a sacred precinct and gymnasium called the "Academy"

The agent believes that everything that agent desires to do aims at something that is at least no worse than the other options the agent thinks are available. Clearly Plato has abandoned KRS and Socratic Intellectualism: he thinks that people often have irrational desires to do things which their rational part says they should not do.

Weakness of Will

In popular Greek morality, this is the notion that sometimes a person might believe that doing X is not really the best available option but do it anyway, because that person is influenced by pleasure, emotion, etc. It is not necessarily the case that at the time the person does X, the person is aware of her belief that it is not the best course of action. We would call it a "lapse of judgment" or perhaps the person just has no particularly carefully thought out notion that X is not the best option, but does it under the influence of emotion, pleasure etc.

Plato's attitude towards poets is that they are indifferent to truth and they aim at pleasing. BUT, in the Apology, Ion, and Phaedrus, he says poets are divinely inspired. And yet, even so, they are unable to assess what the gods inspire in them: even if their poetry contained truth and virtue, etc., the poets would be unable to critically analyze and understand that.

Alcibiades, a brilliant young man, and Nicias, an experienced general, were assigned to the force. Before it left, Alcibiades was implicated in the mutilation of some statues called herms. His trial occurred while he was on expedition, and he was condemned. The Sicilian expedition failed completely and utterly. The Symposium includes as characters Alcibiades, Phaedrus, and Eryximachus, all implicate in the affair of the herms.

Thrasymachus says that justice is benefitting others at one's own expense, Socrates refutes that idea.

399 BCE. Socrates was tried on the basis of two notoriously ambiguous charges: corrupting the youth and impiety. More specifically, Socrates’ accusers cited two ‘impious’ acts: ‘failing to acknowledge the gods that the city acknowledges’ and ‘introducing new deities.’ A majority of the 501 dikasts (Athenian citizens chosen by lot to serve as jurors) voted to convict him. Consistent with common practice, the dikasts determined Socrates’ punishment with another vote. Socrates was ultimately sentenced to death by drinking a hemlock-based liquid.

Echecrates encounters Phaedo of Elis, one of the men present during Socrates' final hours. Eager to hear the story from a first-hand source, Echecrates presses Phaedo to tell what happened.

A number of Socrates' friends were gathered in his cell, including his old friend Crito and two Pythagorean philosophers, Simmias and Cebes. The account begins with Socrates proposing that though suicide is wrong, a true philosopher should look forward to death. The soul, Socrates asserts, is immortal, and the philosopher spends his life training it to detach itself from the needs of the body. He provides four arguments for this claim.

The first is the Argument from Opposites. Death is the opposite of life, and so living things come to be out of dead things and vice versa. This implies that there is a perpetual cycle of life and death, so that when we die we do not stay dead, but come back to life after a period of time.

The second is the Theory of Recollection.

The third is the Argument from Affinity. Socrates draws a distinction between those things that are immaterial, invisible, and immortal, and those things which are material, visible, and perishable. The body is of the second kind, whereas the soul is of the first kind. This would suggest that the soul ought to be immortal and survive death.

At this point, both Simmias and Cebes raise objections. Simmias suggests that perhaps the soul is like the attunement of a musical instrument. The attunement can only exist so long as the instrument exists, and no longer. Cebes admits that perhaps the soul is long-lived, and can outlive many bodies, but argues that this does not show that the soul is immortal.

Socrates replies to Simmias by pointing out that his theory of attunement is in conflict with the Theory of Recollection, which proposes that the soul existed before the body. As for Cebes, Socrates embarks on a complex discussion of causation that ultimately leads him to lay out his fourth argument, positing the unchanging and invisible Forms as the causes of all things in this world. All things possess what qualities they have only through participation in these Forms. The Form of Life is an essential property of the soul, Socrates suggests, and so it is inconceivable to think of the soul as ever being anything but alive.

Socrates concludes with a myth of what happens to souls after death. Then he has a bath, says some last goodbyes, drinks the poisonous hemlock, and drifts imperceptibly from this world to the next.

Apollodorus relates to an unnamed companion a story he learned from Aristodemus about a symposium, or dinner-party, given in honor of the tragedian Agathon. Socrates arrives at the party late, as he was lost in thought on the neighboring porch. After they have finished eating, Eryximachus picks up on a suggestion of Phaedrus', that each person should in turn make a speech in praise of the god of Love.

Phaedrus begins by saying that Love is one of the oldest of the gods, and the one that does the most to promote virtue in people. Pausanias follows Phaedrus, drawing a distinction between Common Love, which involves simple and mindless desire, and Heavenly Love, which always takes place between a man and a boy. In the case of Heavenly Love, the boy, or loved one, sexually gratifies the man, or lover, in exchange for education in wisdom and virtue. After Pausanias, Eryximachus, the doctor, speaks, suggesting that good Love promotes moderation and orderliness. Love does not restrict itself to human interaction, but can be found in music, medicine, and much else besides.

The next to speak is the comic poet Aristophanes. Aristophanes draws an engaging myth that suggests that we were once all twice the people we are now, but that our threat to the gods prompted Zeus to cut us in half. Ever since, we have wandered the earth looking for our other half in order to rejoin with it and become whole. Agathon follows up Aristophanes, and gives a rhetorically elaborate speech that identifies Love as young, beautiful, sensitive, and wise. He also sees Love as responsible for implanting all the virtues in us. Socrates questions Agathon's speech, suggesting that Agathon has spoken about the object of Love, rather than Love itself.

In order to correct him, Socrates relates what he was once told by a wise woman named Diotima. According to Diotima, Love is not a god at all, but is rather a spirit that mediates between people and the objects of their desire. Love is neither wise nor beautiful, but is rather the desire for wisdom and beauty. Love expresses itself through pregnancy and reproduction, either through the bodily kind of sexual Love or through the sharing and reproduction of ideas. The greatest knowledge of all, she confides, is knowledge of the Form of Beauty, which we must strive to attain.

At the end of Socrates' speech, Alcibiades bursts in, falling-down drunk, and delivers a eulogy to Socrates himself. In spite of Alcibiades' best efforts, he has never managed to seduce Socrates as Socrates has no interest at all in physical pleasure.

In The Republic, Plato, speaking through his teacher Socrates, sets out to answer two questions. What is justice? Why should we be just? Book I sets up these challenges. The interlocutors engage in a Socratic dialogue similar to that found in Plato’s earlier works. While among a group of both friends and enemies, Socrates poses the question, “What is justice?” He proceeds to refute every suggestion offered, showing how each harbors hidden contradictions. Yet he offers no definition of his own, and the discussion ends in aporia—a deadlock, where no further progress is possible and the interlocutors feel less sure of their beliefs than they had at the start of the conversation. In Plato’s early dialogues, aporia usually spells the end. The Republic moves beyond this deadlock. Nine more books follow, and Socrates develops a rich and complex theory of justice.

When Book I opens, Socrates is returning home from a religious festival with his young friend Glaucon, one of Plato’s brothers. On the road, the three travelers are waylaid by Adeimantus, another brother of Plato, and the young nobleman Polemarchus, who convinces them to take a detour to his house. There they join Polemarchus’s aging father Cephalus, and others. Socrates and the elderly man begin a discussion on the merits of old age. This discussion quickly turns to the subject of justice.

Cephalus, a rich, well-respected elder of the city, and host to the group, is the first to offer a definition of justice. Cephalus acts as spokesman for the Greek tradition. His definition of justice is an attempt to articulate the basic Hesiodic conception: that justice means living up to your legal obligations and being honest. Socrates defeats this formulation with a counterexample: returning a weapon to a madman. You owe the madman his weapon in some sense if it belongs to him legally, and yet this would be an unjust act, since it would jeopardize the lives of others. So it cannot be the case that justice is nothing more than honoring legal obligations and being honest.

At this point, Cephalus excuses himself to see to some sacrifices, and his son Polemarchus takes over the argument for him. He lays out a new definition of justice: justice means that you owe friends help, and you owe enemies harm. Though this definition may seem different from that suggested by Cephalus, they are closely related. They share the underlying imperative of rendering to each what is due and of giving to each what is appropriate. This imperative will also be the foundation of Socrates’s principle of justice in the later books. Like his father’s view, Polemarchus’s take on justice represents a popular strand of thought—the attitude of the ambitious young politician—whereas Cephalus’s definition represented the attitude of the established, old businessman.

Socrates reveals many inconsistencies in this view. He points out that, because our judgment concerning friends and enemies is fallible, this credo will lead us to harm the good and help the bad. We are not always friends with the most virtuous individuals, nor are our enemies always the scum of society. Socrates points out that there is some incoherence in the idea of harming people through justice.

All this serves as an introduction to Thrasymachus, the Sophist. We have seen, through Socrates’s cross-examination of Polemarchus and Cephalus, that the popular thinking on justice is unsatisfactory. Thrasymachus shows us the nefarious result of this confusion: the Sophist’s campaign to do away with justice, and all moral standards, entirely. Thrasymachus, breaking angrily into the discussion, declares that he has a better definition of justice to offer. Justice, he says, is nothing more than the advantage of the stronger. Though Thrasymachus claims that this is his definition, it is not really meant as a definition of justice as much as it is a delegitimization of justice. He is saying that it does not pay to be just. Just behavior works to the advantage of other people, not to the person who behaves justly. Thrasymachus assumes here that justice is the unnatural restraint on our natural desire to have more. Justice is a convention imposed on us, and it does not benefit us to adhere to it. The rational thing to do is ignore justice entirely.

The burden of the discussion has now shifted. At first, the only challenge was to define justice; now justice must be defined and proven to be worthwhile. Socrates has three arguments to employ against Thrasymachus’ claim. First, he makes Thrasymachus admit that the view he is advancing promotes injustice as a virtue. In this view, life is seen as a continual competition to get more (more money, more power, etc.), and whoever is most successful in the competition has the greatest virtue. Socrates then launches into a long and complex chain of reasoning which leads him to conclude that injustice cannot be a virtue because it is contrary to wisdom, which is a virtue. Injustice is contrary to wisdom because the wise man, the man who is skilled in some art, never seeks to beat out those who possess the same art. The mathematician, for instance, is not in competition with other mathematicians.

Socrates then moves on to a new argument. Understanding justice now as the adherence to certain rules which enable a group to act in common, Socrates points out that in order to reach any of the goals Thrasymachus earlier praised as desirable one needs to be at least moderately just in the sense of adhering to this set of rules.

Finally, he argues that since it was agreed that justice is a virtue of the soul, and virtue of the soul means health of the soul, justice is desirable because it means health of the soul.

Socrates encounters Euthyphro outside the court of Athens. Socrates has been called to court on charges of impiety by Meletus, and Euthyphro has come to prosecute his own father for having unintentionally killed a murderous hired hand. Socrates flatters Euthyphro, suggesting that Euthyphro must be a great expert in religious matters if he is willing to prosecute his own father on so questionable a charge. Euthyphro concurs that he does indeed know all there is to be known about what is holy. Socrates urges Euthyphro to instruct him and to teach him what holiness is, since Euthyphro's teaching might help Socrates in his trial against Meletus.

First, Euthyphro suggests that holiness is persecuting religious offenders. Socrates finds this definition unsatisfying, since there are many holy deeds aside from that of persecuting offenders. He asks Euthyphro instead to give him a general definition that identifies that one feature that all holy deeds share in common. Euthyphro suggests that what is holy is what is agreeable to the gods, in response to which Socrates points out that the gods often quarrel, so what is agreeable to one might not be agreeable to all.

Euthyphro's most important attempt to define holiness comes with his suggestion that what is holy is what is approved of by all the gods. Socrates sets up a rather elaborate argument to show that the two cannot be equivalent. What is holy gets approved of by the gods because it is holy, so what is holy determines what gets approved of by the gods. And what gets approved of by the gods in turn determines what is approved of by the gods. It follows from this reasoning that what is holy cannot be the same thing as what is approved of by the gods, since one of these two determines what gets approved of by the gods and the other is determined by what gets approved of by the gods.

Euthyphro is next led to suggest that holiness is a kind of justice, specifically, that kind which is concerned with looking after the gods. Socrates wonders what Euthyphro means by "looking after the gods." Surely, the gods are omnipotent, and don't need us to look after them or help them in any way. Euthyphro's final suggestion is that holiness is a kind of trading with the gods, where we give them sacrifices and they grant our prayers. Our sacrifices do not help them in any way, but simply gratify them. But, Socrates points out, to say that holiness is gratifying the gods is similar to saying that holiness is what is approved of by the gods, which lands us back in our previous conundrum. Rather than try to find a better definition, Euthyphro leaves in a huff, frustrated by Socrates' questioning.