Why he drank 

The scene is at the end of Plato's Phaedo. Socrates has spent the day arguing with friends about whether the soul survives the body, sends his wife Xanthippe away because of the weeping, bathes, and then takes the cup from the prison officer, who apologises for his job. He drinks steadily and without hesitation. He rebukes his companions for crying, walks until his legs feel heavy, lies down, and the numbness rises from his feet towards his chest while he covers his face. His last recorded words are a reminder to Crito about a debt of a cock owed to Asclepius, the god of healing. Then he is gone, quietly, mid-conversation.

As literature it is one of the great death scenes in any language. As a clinical report it is smoother than the plant allows. Conium maculatum, poison hemlock, contains coniine and related alkaloids that block neuromuscular transmission and produce an ascending paralysis, so the progressive numbness Plato describes is broadly right in shape. But documented poisonings also commonly involve salivation, vomiting, abdominal pain, tremors, difficulty swallowing and sometimes convulsions before respiratory muscles fail. Modern discussions have gone back and forth about how much of Plato's serenity is pharmacology and how much is composition, including proposals that the Athenian preparation was mixed with other substances. What is safe to say is that Plato was writing philosophy rather than a medical case note, and Xenophon, who does not narrate the death at all, gives no help.

The staging is doing deliberate work. The whole dialogue argues that a philosopher spends life practising for the separation of soul from body, so a philosopher's death must be shown as the calm completion of that practice, not as a poisoning. Plato was not present, and says so within the dialogue, which is an unusual thing to include unless the point is that the account is transmitted rather than witnessed.

That leaves the question the chapter title asks. He drank because he had argued himself into a position with no exit: that it is better to suffer injustice than to commit it, that a citizen who has accepted a city's protection cannot break its verdicts at his convenience, and that death is either nothing or a change of place, in neither case an evil for a good man. Consistency was the entire content of his teaching. A Socrates who slipped away to Thessaly would have refuted Socrates more thoroughly than any prosecutor did.

What survived him was not a doctrine but a technique, and it is small enough to use over dinner.