  Thus prompted, Theaetetus states his first acceptable definition, which is the proposal (D1) that “Knowledge is perception” (151d–e). Socrates does not respond to this directly. Instead he claims that D1 entails two other theories (Protagoras’ and Heracleitus’), which he expounds (151e–160e) and then criticises (160e–183c). Socrates eventually presents no fewer than eleven arguments, not all of which seem seriously intended, against the Protagorean and Heracleitean views. If any of these arguments hit its target, then by modus tollens D1 is also false. A more direct argument against D1 is eventually given at 184–7.