Abstract

In this thesis, I present an account of the development of early Greek epistemology, according to which Protagoras' measure doctrine, and his argument from conflicting appearances, was the starting point for work on perception and knowledge by Plato in the Theaetetus, Aristotle in Metaphysics IV and Democritus. In Chapter One, I argue against the assumption that Protagoras' Aletheia contained a philosophical theory. It was probably not a treatise, but a virtuoso show-piece, with the aim of "knocking down" views according to which truth is only known by gods, and, with difficulty, by privileged humans--namely, philosophers. For this, it need not have contained more than some well-chosen examples of perceptual and value beliefs, and arguments that one cannot decide which are true. In Chapter Two, I argue that Democritus should be seen as Protagoras' heir. Democritus argued Protagoras' general claim is self-refuting, but thought he was right about perceptual appearances. In Confirmations, he defended the senses, attributing to them knowledge and "power of proof." However, his theory led to an ancestor of the primary/secondary quality distinction, and this threatened to undermine the theory itself because of implications--that one can only know how things appear and not how things are by nature--which were later taken up in Pyrrhonist skepticism. In Chapter Three, I present a reading of the Secret Doctrine in Plato's Theaetetus as a defense and diagnosis of Protagoras' claim, in particular, an explanation of the global relativization which Protagoras' claim seems to recommend. This reading is meant to avoid the well-known difficulties concerning the prevailing interpretation of Protagoras' "Secret Doctrine" as a flux doctrine. I also argue that Plato developed the Secret Doctrine with Democritus in mind. In Chapter Four, I argue that Plato's "self-refutation argument" is aimed at relativism, but not relativism about truth. The latter, which Aristotle dismisses as eristical, is a position Protagoras can take, but Plato's argument works against it as well. In Chapter Five, I examine why Aristotle seems to treat Protagoras in Metaphysics IV as being committed to a denial of the principle of non-contradiction.