The Parmenides describes a young Socrates meeting the Eleatics Parmenides and Zeno around 450 BCE, an impossible event that would have been quite significant but no ancient historian before or after Plato mentions.  The Theaetetus mentions this meeting, and then the Sophist and Statesman each refer to the previous dialog, building on the continuing discussion.  Many have noticed that the Theaetetus displays Plato’s later style, which Plato used to attract more philosophy students to his Academy of Athens and Platonic philosophy of the immortality of the rational mind and forms of knowledge.

In several dialogues, Plato’s Socrates argues that if there are eternal forms we can know with our minds, such as the ratios of math and music, then the rational mind is immortal.  When we withdraw from the senses, we can grasp the forms of things with thought, much as we can see someone doing something good but cannot see the goodness itself and must think it to hold it in mind and compare it to other things.  However, this creates a problem: how are particular things we can sense related to the forms of things we can’t sense but can think? Parmenides confronts young Socrates with this unsolved problem in Plato’s Parmenides.

In the Theaetetus, following the Parmenides, Plato’s Socrates argues that we cannot know similarities and differences between sensible, mortal things without knowing the super-sensible, immortal forms of things.  Then, in the Sophist, following the Theaetetus, he argues that we can know similarities and differences between the forms themselves.  Thus, the questions about the relations between sensible things that boy Socrates cannot answer in the Parmenides are answered in the Theaetetus, and then the questions about the relations between the forms themselves are answered in the Sophist, where Socrates also contrasts sophists such as Gorgias and Protagoras with genuine seekers of knowledge beyond the Heraclitean flux of sensibles in the world of shadows below.

In Plato’s dialog the Theaetetus, shortly after Socrates’ death, Eucleides and Terpsion, friends of Socrates who were at his side in Plato’s Crito, morn that Theaetetus, a courageous warrior (and later a notable student of mathematics in Plato’s Academy), is suffering from dysentery and near death.  Eucleides says that Socrates met young Theaetetus before Socrates’ death, conversed with him, and foresaw through prophetic insight that Theaetetus would become the remarkable man he is.  Terpsion asks if Eucleides can repeat the conversation, and Eucleides says he can’t recite it from memory, but he took notes that he and Terpsion should listen to his slave boy read it to them at his place.  Thus, we have a play within a play.

In the central dialog, Socrates asks Theodorus, a mathematician known for lectures about geometry, if the young people from his hometown devote themselves to geometry and knowledge.  Theodorus says yes, that he knows one boy who is brilliant, and that he would hesitate to speak if the boy was beautiful, as he could be accused of being in love with the boy, but the boy is rather ugly, much like Socrates himself but not as ugly, as Theodorus is somewhat embarrassed but not too embarrassed to say.  He tells Socrates that the boy is unlike anyone he has met before, which presumably includes Socrates himself, with a quick wit and a gentle spirit, a good mind and a good heart.  Generally, those with great minds have untamed hearts, are quick to love and hate but unsteady and undetermined, while those with strong, confident hearts are even-keeled but often dull and stupid.  This boy, however, is smooth like a stream of olive oil, brilliant but smooth, quiet and steady with insight.

Theodorus sees the boy, young Theaetetus, coming towards them with his friends, and helpfully tells Socrates that the boys have been oiling themselves up outside and seem ready to do whatever it was that they were oiling themselves up for, perhaps wrestling.  Theodorus asks Theaetetus to sit with Socrates and talk to him, and Socrates tells Theaetetus he wants to test him to see if he indeed has a character like that of himself. Theodorus said none were better than this kid, just as the oracle said of Socrates, and this conversation is supposed to be happening just before Socrates’ trial, where he tells everyone he has to question everyone, as the oracle asked him to do, to see if he is wisest.

Socrates begins by stating, and Theaetetus agrees in yes-man style, that if they each had a harp, what the Greeks called a lyre, what the Cretans confusingly say of themselves, if Socrates played a note, and Theaetetus played the same note, if Theodorus was just anybody they would not trust him to judge that they are tuned to the same pitch, but if Theodorus was a musician, with expertise and experience, they would both trust his judgement.  Socrates has been compared to Theaetetus indirectly, judged to be similar by Theodorus, and Socrates says that Theodorus is an expert in intellectual matters, and so Socrates should trust his judgement and examine Theaetetus, whom Theodorus has praised above everyone.

Socrates says there is one small matter which Theaetetus and the others can help him think out:  Learning something makes us wiser, but does this mean that knowledge and wisdom are the same thing, that gathering knowledge and understandings is the same thing as reason and insight?  In the context of Plato’s dialogues, we can ask: Does taking positions and counter-positions in arguments with everyone teach us anything, or help us to think? Heraclitus says yes, but wisdom is beyond all human knowledge and positions, while Parmenides says no, because knowledge is an illusion and wisdom is silent, without division, and doesn’t move, or at least contradicts itself with complete and cosmic consistency.  Both would agree that wisdom is not simply words and human understandings attached to them, but Theaetetus says yes, they are the same thing.

Socrates says he is still puzzled, as they will have to understand knowledge first before determining if it is identical with wisdom, much as Theodorus is an expert on mathematics, so he ought to know if Socrates and Theaetetus have similarly tuned minds and hearts.  Socrates tells everyone they will each take turns speaking, as boys take turns in a ballgame, and if they miss they have to sit out, but if a boy does not miss he gets to be king and ask any questions he likes of the others. Socrates might fancy himself such a king, questioning children all over Athens.  Theodorus says he is not at home in abstract discussions himself, but encourages Socrates to question everyone and improve the minds of the youth. At Socrates trial, which happens just after this, he is specifically accused of corrupting the youth, whether or not the youth are pre-oiled.

Socrates says that if we want to know what clay is, we can’t say that clay is made into pots by the potter, and bricks by the brick-maker, and ovens by the oven-master.  Similarly, we can’t say what knowledge is and understand it by saying there is the shoemaker knowing how to make shoes, the furniture-maker making furniture, and the doll-maker making dolls, but rather what is the common stuff of it.  Socrates says that clay is earth mixed with water, basic elements that are solid and fluid, not whose clay it is or what it is used for.

Theaetetus says this is remarkably like a point he made to Theodorus as he was teaching them geometry the other day, when he and the other boys realized they could group numbers into square numbers and rectangular numbers, such that four is square but three and five are not.  Numbers can be divided into squares and rectangles, just as clay can be divided into earth and water, solid and liquid, but Theaetetus says he cannot answer the question of knowledge by similarly dividing it into two parts, and so perhaps Theodorus was wrong to say that he was as wise as Socrates.

Socrates says that if Theaetetus beat him in a race, they could say he was faster, but neither of them have bested the other, as neither know what knowledge is, at least yet, and he proceeds, as he did with the slave boy in the Meno, to lead Theaetetus and himself to an answer together, but one that doesn’t end up satisfying Socrates to his own liking.  Theaetetus says that he has never heard anyone answer the question of what knowledge is, but he has often thought about it and can only tell Socrates about how he feels.

Socrates says that his mother was the full-chested midwife Phaenarete, the mom of Socrates, and that he is also a midwife, an elder who is past childbearing years who helps others conceive children, but unlike most midwives any of us would consider hiring, he tests the children to see which of them are real children and which of them are mere ghosts.  Socrates says the heavens, the gods, forbid him to have his own ideas, but rather to lead others into having them. Soon after this, Socrates will be accused of atheism at his trial.

Theaetetus is pregnant with a possible idea, which Socrates will help him to conceive and then test, because, as a midwife, Socrates can tell that this oiled-up boy is pregnant.  Also, Socrates says he works with men, who have ideas, not with women, who make babies, and that men having ideas suffer distress far greater than women making babies. Clearly, Socrates’ midwife mother taught him much.  If Theaetetus has a miscarriage, Socrates will throw out the child-idea, but asks that Theaetetus not act like a woman who just lost her firstborn when he does it. Socrates often destroys the initial ideas of his debate partners, as he did in the Symposium all around.  Thus, Socrates asks Theaetetus to take a shot at defining knowledge, possibly to shoot him down.

Theaetetus starts where Hegel did thousands of years later in Germany, with sense-certainty, such that knowledge is perception and observation.  The American expression right as rain sums up sense-certainty, that, as an American judge once said in court attempting to define obscenity and thus pornography, I know it when I see it.  Socrates says that this is what Protagoras meant when he said Man is the measure of all things, including midwives and childbirth apparently.  If the wind makes one man cold and another man not cold, then the wind is perceived to be, appears to be and to Protagoras is both cold and not cold, known in two divergent ways.

Socrates wonders if Protagoras was secretly ingenious, and throws out this obscure saying to benefit the common herd, like themselves, and kept the truth as a secret doctrine he reveals only to his closest students.  Socrates suggested the philosophers who lead society lie to the lower classes in the Republic in a similar way, but anyone who has read Protagoras text Truth at the time would know that Protagoras opens with the statement Man is the measure of all thingsand does not mean to be obscure or cryptic about his relativism at all, stating it clearly up front.

Socrates says that Protagoras possibly kept the idea that things can’t simply be large and not small, or heavy and not light, or simply be any particular thing, because all things are in a process of becoming, of being and not being, and this is what all the ancient great philosophers except Parmenides, including Protagoras, Heraclitus and Empedocles.  Even the poet Homer, who Socrates calls the captain of the team, said that the ocean was the father of all things. If team Homer-Heraclitus is right, then all things are made of fire in flux, and this means that knowledge too would have to be in motion, just as all things are stirred in circles by the “golden rope” of the Sun’s cycle. Socrates asks Theaetetus:  Who could take on such a team with such a captain? Theaetetus says it would be no light undertaking. This is, of course, what Socrates is saying they will do, without directly saying it.

Socrates presents Theaetetus with many dizzying puzzles of relativism that many critics think do not present much of a clear point, before asking Theaetetus to look around to make sure that none of the “uninitiated” can hear them, those who think that only visible things are real.  Socrates is doing what he suggests Protagoras was doing, withholding knowledge from those who are not ready for the real teaching, but he is playful about speaking of it openly with children. Those who do not believe in invisible things are crude, but Team Homer is refined, and Socrates will initiate Theaetetus into their secrets, mocking them sarcastically for being crude but also obscure in teaching people that only moving things are real, and anyone who says otherwise is incorrect.  Theaetetus is not sure if any of this makes sense, in spite of his initiation, and he doesn’t know if Socrates believes it or is simply testing him.  Socrates says that he is helping Theaetetus to come to his own idea of it, and Theaetetus says Socrates does present the idea as quite reasonable. It is unstated but obvious that Socrates is playing the best devil’s advocate for his opponent’s position, and does not include himself with Team Homer, but rather excludes himself, like he does Parmenides, from it.

Socrates says that they can doubt whether or not their conversation is merely a dream or a delusion, and they have no test to prove things one way or the other, as the test would be part of the dream or delusion, and if you dream that you are flying, you truly have the experience you have.  However, if we taste wine as sweet when we are healthy and sour when we are sick, does this mean that you are a different person when you are sick? Protagoras would have to say that we have been infinite people, ever-changing, and that no one ever has the right to tell anyone that they are wrong about anything, as there are no standards against which to measure right judgement if everything is real to the one who perceives it.

Socrates concludes that Theaetetus’ idea that perception is knowledge is the same as Tribe Heraclitus’ ideas that all things are in motion and we are their measure.  This is the idea of Theaetetus that Socrates has helped him carry to term, which means in phase two Socrates will now test Theaetetus’ idea, which the boy did volunteer but not develop much at all in the course of Socrates’ rant about Homer and crew.  Testing it, Socrates will find that the idea is a mere phantom, not a real child, unlike the wonder-boy Theaetetus. Socrates says they should carry their child around the fireplace, as is traditionally done, to examine it from every angle.

Socrates says that philosophers, who seem clumsy and stupid to most people, are concerned with real, eternal, higher things, such as beauty and knowledge, not the scandals in the next house over, which is why they often can’t feed themselves or make their own beds.  Perhaps Plato is thinking of the absent-minded Thales, and Theodorus did say that many great minds, unlike Theaetetus, are not even-keeled. Later, Aristotle will argue that true philosophers should simply think, and have everything else taken care of for them.

Socrates says that we hear the sounds of a foreign language, but we do not understand them and foreigners do, such that the foreigner hears the sounds and knows what they mean, but we hear the sounds and don’t.  It is the same with written languages as well, and this shows us that perception and knowledge are very much two different things. This would also have been a wonderful example for Socrates, who says he has no ideas while having many of them, to have mentioned before telling Theaetetus that he’s stuck with the earliest idea they both had together as Theaetetus’ own kid, who now suddenly appears, immediately after conception, to be fake.

Theaetetus says that we could argue that after perceiving language classes, we would perceive the sounds of a foreign language differently, so Socrates turns to memory, and asks if we still know things when we no longer perceive them.  Theaetetus has to agree that we do know things that we are not seeing with our eyes or remembering with our mind, or he commits himself to the view that when we shut our eyes, we don’t know much of anything. Unfortunately, this means he can’t say that remembering things is re-perceiving them, as we can remember things we don’t perceive.  Socrates adds that we can see things dimly or keenly, and these degrees of perception do not have much to do with whether or not we know the thing we are perceiving dimly or keenly. We can imagine, for instance, seeing apples at dusk, and yet having a particularly brilliant and keen knowledge of them, acquired from debates with oily children.

Socrates says that Protagoras cannot defend himself as wise, or his relativism as correct, as he would have to admit on the stand, where Socrates will soon be, that any imbecile is just as correct in their judgements as he is.  Protagoras is an ignorant pig, and can’t prove himself otherwise a man. Protagoras also is possibly the first to call himself a “sophist”, a wisdom-ist, claiming to have superior wisdom, and Plato continues on in the sophist to determine the difference between what Plato thinks is a genuine, truthful philosopher and a false, deceptive sophist.  Our word sophistry still means sophisticated reasoning, but deceptive and false.

Plato presents the sophists as immoral philosophers for hire, who will argue anything for anyone, for a fee, like a high-priced lawyer.  Protagoras taught rhetoric for a price, and Plato presents Socrates as the one who can first argue for, and then argue against Protagoras, just as Parmenides told him to do for years to train in thought and debate.  Socrates argues further, fitting with fees and tutoring the rich in rhetoric, that Protagoras has no position against might makes right, that truth is nothing but power over others, enforcing one’s will on others, if man is the measure of all things.  This is what Socrates spent the entire Republic attacking, the pessimistic claim of Thrasymachus that there is no other good to pursue in the world.

Theodorus brings up Heraclitus, now that Protagoras has been soundly defeated, and says that his followers violently passionate and you may as well try to debate with a maniac.  They are always in motion, and so they can’t be pinned down, and if you ask them a question, they fire several arrows swiftly, one after another, from their quiver of quotations and sayings, leading from one meaning to another, and from one metaphor to another.  You can never get anywhere with them, because they refuse to stand still.

Socrates brings up Parmenides, says Parmenides is in opposition to the Homer-Heraclitus traveling circus, but when you try to talk to Parmenides, which Socrates reminds us he did as a boy, in the last dialogue, and it is similarly impossible to talk to him about knowledge, as the One is indivisible and immobile and so nothing else can be said.  Between these two lines of warriors facing off, they are being pulled in opposite directions.

Theaetetus says he has heard that an account with judgement is knowledge, and that things that can be accounted for, unlike those that are unknowable, are indeed knowable.  Socrates says that giving an account of something is to make our thoughts vocal with words and expressions, and that vocalizing judgements depends on referencing the primary elements of the subject.  We can go through a wagon part by part, primary element by primary element, just as we write words letter by letter, such that we find “the way to the whole through the parts,” as if there is a set number of things to know, such as the forms, and an order through which to know them.  Third, and lastly, we can say in an account of things how each is different from other things, such as the Sun, the brightest thing there is.  Thus, while the eternal forms and their differences are left for future discussions, we have a route laid out to know them, possibly.

Socrates concludes with Theaetetus that they have both failed to produce a complete understanding of perception and its relationship to knowledge.  It goes unmentioned that this is because the eternal, ideal forms have yet to be presented, leaving things in a state of confusion. And with that, Socrates says he has to get to court about some sort of trial, and that he and Theodorus should meet again tomorrow.  Hopefully all of that worked out.