Plato's philosophy is profoundly indebted to Socrates. This is especially true of the so-called 'aporetic dialogues', which leave the reader with puzzles but no positive views. As soon as we turn to Plato's doctrines, however, it becomes clear that he is building on the views of practically all major early Greek thinkers: Parmenides, Heraclitus, Protagoras, the Pythagoreans, Anaxagoras, Empedocles. We will read ca 10 of Plato's dialogues and a number of Presocratic fragments in order to identify and highlight the nature of this philosophical discussion, without forgetting Socrates himself.