Plato's Theaetetus

Plato's Theaetetus addresses the question "What is knowledge?" Three main answers are offered:

1. Knowledge is Perception (151d-186e)
   • Protagorean Relativism (15le-152c)
   • Heraclitean Flux (152c-157d)
   • The problem of dreams (157e-160e)
   • Three objections to Protagorean Relativism and Knowledge is Perception (160e-168c)
   • Refutation of Protagorean Relativism using it to refute itself (170a-172c, 177c-179b)
   • Refutation of Heraclitean Flux (179c-183c)
   • Refutation of Knowledge is Perception (183c-186e).
2. Knowledge is True Belief (187a-201c)
   • Refutation of Knowledge is True Belief (200d-201c)
3. Knowledge is True Belief with an Account (201d-210d)

Plato considers the doctrine that knowledge is perception to be "the same thing" as Protagorean Relativism and "the same thing" as Heraclitean Flux (160d).

Burnyeat's article asks the question: are the doctrines of Protagorean Relativism and Heraclitean Flux things that Plato refutes considered in relation to knowledge but accepts as doctrines about the sensible world? Or are they merely supports for the doctrine that Knowledge is Perception and considered refuted completely even for the sensible world?

Burnyeat defends the claim that Protagoras thought that no beliefs whatsoever are true flat out: they are all only true for the believer who holds them. That makes Protagoras a thorough relativist.

Gail Fine (see footnote 80 in Intro to Plato 1), however, has defended the view that Protagoras thinks all beliefs are true simpliciter (flat out): in other words, my beliefs are not just true "for me," but flat out true. In other words, my beliefs are infallible knowledge.

A further question is whether these theories apply to A) perception alone, B) perception and all (non-perceptual) belief, C) perception, (non-perceptual) belief, and knowledge, or D) Some other combination of some or all perceptions, beliefs, and knowledge?

As for Heraclitean Flux, after having critiqued Heracleitean flux, is Plato now claiming that nothing at all is in Heraclitean Flux, or rather that some things are or may be, but knowledge cannot be in Heraclitean Flux? Perhaps he is claiming that TRUTH cannot be, and since TRUTH cannot be of anything that does not have BEING, that BEING too cannot be subject to the FLUX.