Socrates never wrote anything down
Not a line. Everything attributed to him comes from other people — mostly PLATO, who wrote dialogues with Socrates as the main speaker, plus a soldier called Xenophon and a comic playwright who put him on stage being ridiculous.
Scholars call this the Socratic problem, and it has no solution: there is no way to separate the historical man from the character Plato used to argue his own case. The most influential figure in ancient Greek thought may be substantially a literary invention by his student. What survives of him is a method rather than a doctrine — keep asking the person what they mean until the answer falls apart.
He could have taken exile and asked for free dinners instead
In 399 BC Athens tried Socrates for impiety and corrupting the young. Convicted, he was invited under Athenian procedure to propose his own punishment, and everyone expected exile, which the jury would probably have accepted.
He proposed that the city should instead give him free meals for life in the town hall, the honour normally reserved for Olympic champions, on the grounds that he had done Athens a service. He then offered a small fine. The jury voted for death by a wider margin than it had voted to convict. Friends arranged an escape and he declined that too, arguing that a citizen who accepts a city's laws when they suit him cannot break them when they do not.
Philosophy keeps giving away its best questions
For most of history, philosophy was the study of everything. What is the world made of, how do bodies move, how does the mind work, what makes an argument valid — all philosophy. Then each question, once it becomes answerable by experiment, leaves and sets up on its own.
Natural philosophy became physics and chemistry. Psychology split off in the 1870s when someone built a laboratory for it. Logic, worked on by BACON, Gottlob Frege and RUSSELL, turned into the mathematics that computers run on. Economics walked out through MILL and MARX. What is left in the department is the set of questions nobody has yet worked out how to test, so philosophy always looks as though it is making no progress. It is the part that has not graduated yet.
Different questions, different centuries
The grid is not one conversation. CONFUCIUS was working out how a society holds together through obligation and ritual; SENECA and EPICURUS were writing practical advice on how to live and what to fear; AQUINAS was reconciling Aristotle with Christianity; DESCARTES was trying to find one thing he could not possibly be wrong about, and got as far as the fact that something was doing the doubting.
Then LOCKE, HUME, ROUSSEAU, VOLTAIRE, SPINOZA, PASCAL and KANT on knowledge, government and the limits of reason; HEGEL, NIETZSCHE, MARX and SARTRE on history, meaning and what to do once the old certainties go. ARISTOTLE is in here for very nearly all of it — he wrote on physics, biology, poetry, logic and ethics, and was taken as the final authority on each for about 1,800 years, which is the longest anybody has ever been believed.