This paper is a test case for the claim, made famous by Myles Burnyeat, that the ancient Greeks did not recognize subjective truth or knowledge. After a brief discussion of the issue in Sextus Empiricus, I then turn to Plato's discussion of Protagorean views in the Theaetetus. In at least two passages, it seems that Plato attributes to Protagoras the view that our subjective experiences constitute truth and knowledge, without reference to any outside world of objects. I argue that these passages have been misunderstood and that on the correct reading, they do not say anything about subjective knowledge. I then try out what I take to be the correct reading of the passages. The paper concludes with a brief discussion of the importance of causes in Greek epistemology.