Plato, Republic: Thrasymachus’ Challenges

Posted: Wed, Jan 28, 2026

Today

  • Wrap up course logistics
  • Introduce the Republic
  • Thrasymachus’ challenges

The Repubic’s subject matter

Plato (born c. 427 BCE) grew up during the Peloponnesian War (431–404 BCE).

  • Male Athenian citizens (not women, slaves, or foreign residents) participated in direct democracy and were assigned offices by lot.
  • In the wake of the disastrous Sicilian Expedition, an oligarchical Council of the Four Hundred overthrew democracy in 411 BCE but was soon replaced by a more moderate Five Thousand until democracy was restored in 410 BCE.
  • After Athens fell in 404 BCE, Sparta imposed another oligarchy the Thirty Tyrants, whose bloody rule was again overthrown the following year.
  • The restored democracy tried and executed Socrates in 399 BCE.

Dikaiosunē (adjective: dikaios): “Righteousness”; “justice” (common rendering); “morality” (Waterfield trans.). [Sitong]

  • A notorious headache for translators.
  • While today we follow a long modern tradition of Western political philosophy in thinking of justice primarily in relation to rights, equality, liberty, etc., dikaiosunē is first and foremost a virtue of our character (its opposing vice pleonexia) akin to courage, wisdom, etc.
  • The ancient Greek conception of morality also sweeps broadly to encompass the good life generally—e.g., temperance with respect to bodily pleasures is a moral virtue, whereas its excess (self-indulgence) and deficiency (insensibility) moral vices.
  • The ethics–political philosophy border wars.

The elaborate stage-setting

Harbor scene

  • Socrates and Plato’s brother Glaucon are chilling at a festival down in the Piraeus.
  • They get bullied (?) teasingly (?) into having dinner by Polemarchus and his entourage, among whom is Plato’s and Glaucon’s brother Adeimantus.

Cephalus scene

  • At Polemarchus’, they meet his dad Cephalus, his brothers Lysias and Euthydemus, and the sophist Thrasymachus, among others.
  • Cephalus is a materialistic business guy. He says he now wants to talk with Socrates more often now that he’s too old to have sex with women, drink, feast, etc.
    • Compliment or jibe?
    • Cephalus does not know, but his whole family is about to be ruined following Athens’ surrender to Sparta; Polemarchus would be executed and Euthydemus exiled.
  • Cephalus seems to give us the common sense view (the “folk intuition”) of dikaiosunē:
    • Even though he inherited his wealth, he purports to have made it himself.
    • He thinks he’s getting to live peacefully in retirement not so much because he’s rich (he is rich) but because he’s learned temperament.
    • “A good person wouldn’t easily bear old age if he were poor, but a bad one wouldn’t be at peace with himself even if he were wealthy.” (330a)
    • Justice/morality is about telling the truth, not stealing, paying one’s debts, etc.
  • Plato’s Socrates uses elenchus/the Socratic method on him: “Everyone would surely agree that if a sane man lends weapons to a friend and then asks for them back when he is out of his mind, the friend shouldn’t return them, and wouldn’t be acting justly if he did.”
    • Socrates wants a definition of what justice/morality is, not an unorganized list of examples of just/moral actions.
    • The definition has to be explanatorily prior to the examples; it must tell a plausible story of why all examples of just/moral actions are just/moral in the first place.
    • Socrates often deliberately misunderstands the view being considered to provoke clarifications.

Polemarchus scene

  • Polemarchus jumps in to defend Cephalus/common sense. He clarifies the view: “He means that friends owe it to their friends to do good for them, never harm.”
  • Socrates introduces the skill analogy. [Eduardo]
    • A skill (technē) is directed at an end; to perform a skill well is to achieve its end well.
    • The end of medicine is health; to practice medicine well/to be a good doctor is to treat the sick well.
    • What is the end of being right/just/moral? In other words, what’s being right/just/moral good for?
    • The best answer Polemarchus could come up with is money.
    • But of course there are far better ways to make money.
    • We get a reductio ad absurdum: Surely we shouldn’t believe in common sense morality/justice if it implies being moral/justice is useless?
  • Polemarchus does not give up, and we go through a few more (fishy) rounds of back and forth, until Polemarchus is backed into a corner. So much for conventions.

Back and forth with Thrasymachus

Thrasymachus (noted sophist): Silly, justice/morality is “the advantage of the stronger.” [Sophia]

  • At least two interpretations of the view come up during the exchange (typical of Plato to portray a sophist as confused and misleading).
  • Stephen Miller’s unironic interpretation: “[Y]ou can talk all you want about international niceties and everything else, but we live in a world, in the real world, Jack, that is governed by strength, that is governed by force, that is governed by power; these are the iron laws of the world that have existed since the beginning of time.”
  • A realist “Nietzschean” interpretation: “[M]orality and right are actually good for someone else—they are the advantage of the stronger party, the ruler—and bad for the underling at the receiving end of the orders.”

Thrasymachus’ first challenge: Does might not make right?

  • Socrates introduces two additional assumptions:
    • Stronger = Ruler: Whoever is the actual ruler is the stronger.
    • Fallibility of the Ruler: Rulers make mistakes and sometimes make laws against their own interests.
  • The problem is revealed: On Thrasymachus’ own definition, justice/morality is sometimes the advantage of the weaker.
  • Clitophon throws Thrasymachus a rope—“the advantage of the stronger is what the stronger believes to be his advantage.”
    • Clitophon flattens Thrasymachus’ view back to the conventional wisdom that justice/morality is following the law.
  • This gets really interesting: Thrasymachus dramatically rejects Clitophon’s revision.
    • Infallibility of the Stronger: A stronger who errs is no stronger at all.
    • Thrasymachus then clarifies that he denies Stronger = Ruler.
    • So, even when the ruler makes a law against his own interests, it is still to the advantage of the stronger.
    • This is a very funny view, and he appeals to the skill analogy to defend it: Doctors, accountants, grammarians, etc. who make mistakes are no doctors, accountants, grammarians. (Huh?)
    • But he signs onto the idea that ruling is a skill.
  • So, skills again: Toward what advantage is a skill oriented?
    • No skill seeks its own advantage: Medicine is directed at the advantage of patients, not medicine itself.
    • Likewise, ruling is directed at the advantage of the ruled, not ruling itself.
    • Thrasymachus: Silly, medicine is directed at the advantage of doctors, not patients. “You must look at it as follows, my most simple Socrates: A just man always gets less than an unjust one.”

Thrasymachus’ second challenge: Why should I be just/moral?

Socrates gives us three scandalously sketchy arguments:

  • The argument from knowledge (349a–350e)
    • Thrasymachus: The unjust person is clever and the just person foolish.
    • An unjust person wants to “outdo” a just one.
    • So a clever person would want to “outdo” an ignorant one.
    • But of course it is the knowledgeable person who wants to “outdo” an ignorant one.
    • Thrasymachus is not allowed a comeback; he instead blushes in humiliation.
    • Why suppose the unjust person is guided by the same end as the just person?
  • The argument from strength (351a–352c)
    • Thrasymachus: The unjust person is strong and the just person week.
    • Socrates: Does justice make one weaker or stronger?
      • Injustice leads to hatred and conflict and chaos between persons.
      • Injustice further leads to hatred and conflict and chaos within one person (“a state of civil war”). (Why?)
  • The argument from function (352d–354c)
    • The function/work (ergon) of a knife is to cut; its virtue/excellence (aretê) is what enables it to function well, i.e., sharpness.
    • The function of the soul is living—managing, planning, deliberating, etc.
    • The virtue of the soul is justice.
    • So, justice is what enables the soul to function well.
    • So, justice enables us to live well.
    • So, justice pays.