Notes on Robin Waterfields translation of Platos' Theaetetus.

Part 1: Knowledge as Perception

[151d-186e] Theaetetus, along with a geometer called Theodorus are discussing the question what is knowledge with Socrates on the eve of Socrates' trial for the alleged corruption of young minds and subsequent death at the hands of the Athenian authorities. Its of Platos later period dialogues and is perhaps the first book to tackle the subject of epistemology on its own terms. Plato never gives any definitive answers but his questions turn the matter over like a rock in the hands of a small child to reveal a deliciously wriggly underbelly.

Theaetetus' initial stab; an enumeration of things people know how to do, cobbling is knowledge of making shoes, geometry knowledge of triangles etc is summarily dismissed by Socrates (146e). He hasn't asked what the objects of knowledge are but what knowledge itself is.

The dialogue is full of amazing images and ironies. Twists and turns where Socrates is at one moment delighted and the next deeply depressed upon realising he has made some mistake or other or arrived at a contradiction in his own reasoning.

This post addresses the first of three answers given by Theaetetus to Socrates' question: What is knowledge?

Protagorean Relativism 

Theatetus offers his first proper answer, knowledge is perception. Debate then begins in earnest. This he has learned from the originator of this theory, the sophist Protagoras, probably from reading his book 'The Truth' which no longer exists. Socrates is delighted. He has much respect for Protagoras and believes the idea well worth a pitch fork. For Protagoras 'man is the measure of all things'. Knowledge is relative to the perceiver. What is true for me is and there can be no false beliefs. If I believe the wind is cold and you feel it as hot then we are both right. Borrowing (heavily) from the essay by the translator there are three entailments of this type of relativism:

1. Subjectivism: the wind is neither cold nor warm. I perceive (and so know) it to be cold. You perceive (and so know) it to be warm.
2. Objectivism: the wind itself is both cold and warm. I perceive/know its coldness, you its warmth.
3. The secret doctrine: there is no such thing as wind. There is only the wind as it appears for me, hot cold whatever.

Socrates equates Protagoras' relativism and Heraclitean flux as he feels they entail one another. This is called (by the scholars) the Flux Theory of Perception FTP. The theory of flux maintains the cosmos and everything in it is constant state of motion  The weak form, stated by Heraclitus 'you can't step into the same river twice' and the stronger form attributed to Cratylus is 'you can't step into the same river even once'. 

One of the problems Plato identifies with FTP is that if everything is changing nothing can be identified. I become a different person from one moment to another. I can only know momentarily - at the instant of perception.

Its interesting that the Greek word for perception 'aisthesis' meant either sensation or perception. It is Plato in fact who seems to be the first to recognise the distinction here. Not content with just attacking the version of Protagorean relativism which says knowledge is sensation he attempts to first make the argument he is attacking as strong as possible by allowing for perceiveing to include the forming of beliefs based on the sense data experience.

Protagoras Defeats Himself

In a key section (169d-172b), apparently much debated, Socrates shows that Protagorean relativism is self defeating. My crude version is if I believe A and you believe not A then we are both correct according to the relativism (what is true for me is true for me) but on the other hand how can we both be right if we believe the contradiction of one another. I'm either right now holding up my left hand or I'm not holding up my left hand. 

Platos actual argument is more sophisticated and involves considering Protagoras' belief against the belief of others plural and weighs a multitude believing some propostion is true against Protagoras believing it is not true and then make the proposition the truth of his own book - 'The Truth'; the irony not being lost on Plato. Protagoras holds (and his relativism entails) democracy to be literally majority opinion.

At another point he has Socrates consider the role of expert. He forces Protagoras to  concede that there are such people as experts - he has to in a way as he was a highly paid teacher. The difference is that expert for Protagoras is someone who simply makes someone see something as good whereas a Platonic expert makes someone see the good in something. Once Plato has established expertise as part of Protagorean vocabulary he points out that he must therefore be committed to the truth of other peoples opinions. 

He wraps it up in typical style by saying 'therefore no dog nor ordinary person is a measure of anything at all unless he understands it'.

According to Waterfield whether the logic of Platos actual argument is watertight is debatable but the argument does reduce Protagorean relativism to absurdity and solipsism. Solipsism being the extremely sceptical philosophical position that nothing (i.e. external reality) exists outside of ones own mind - its a curious position adopted by some that is simultaneously indefensible and irrefutable!