The Question of expertise is introduced.	Soc.Yes, pray do, Theaetetus, if only that I may get a good sight of my own likeness; for Theodore tells me I have a face like yours. Now suppose each of us had a lute, and he said they were both tuned to the same pitch; should we at once believe him, or should we have considered whether the man who says so skilled in music? Theaet. We should have considered. Soc. And if we found that he was, we should believe him; or, if ignorant of music, we should put no faith in him. Theaet. True. Soc. So now, I suppose, if we care at all about our faces being alike, we must consider whether the person who says so is conversant with lines, or not. Theaet. I think he is that. (p. 6)
Hidden assumption:  there are objective objects of knowledge. In wisdom, (i. e., the objects of learning) one can be wise.  Objects of learning make learning possible. Lets interpret science here as expertise. Possessors of expert knowledge are wise, re: the subject for which they possess knowledge, if that expert is truly knowledgeable. As if   Science = wisdom.	Soc. . . . And now tell me; is not learning the becoming wiser in what one learns? Theaet. Of course. Soc. And it is in wisdom that the wise are wise. Theaet. Yes. Soc. Now, is there any difference between this and science? Theaet. Of what do you speak? Soc. Wisdom. If we have accurate knowledge on any subjects, are we not also wise in them? Theaet. Of course. Soc. Then science and wisdom are the same. (p 7)
How are we to understand the precise meaning knowledge?	Soc. This then is precisely the point that I am perplexed about, and unable to realize as I should wis h in my own mind, what accurate knowledge is. (p 8)
1^st definition:  Define knowledge as a list of the objects of knowledge that are addressed in various areas of expertise.	Theaet. Well, then, I think that what one can learn from Theodore may be called sciences, geometry and those you just named; and again, shoe-making and the trades of the other craftsmen, all and each of them, are nothing else than knowledge. (p 8)
Objection: A list of particulars cannot be adequate provide a general definition.	Soc. But, my Theaetetus, the question asked was not this, of what things Knowledge is the science, nor how many sciences there are. For it was not with any wish to count them that we asked, but to get a clear knowledge about science, what it is in the abstract. Or is there nothing at all in what I say? (p 9)
Socrates provides a paradigm example of the form of answer he requires.  Anticipating Aristotle insight we ask, “What are the necessary and sufficient condition for something to be what it is and not another thing?”	Soc. . . .  For instance, in the question about clay, it was obvious, surely, and simple to reply, that earth mixed up with any fluid would be clay. (p 10)
Theaetetus draws an analogy between the way one defines clay and his experience of discovering rules of generalization in geometry.  But, he is not confident that we will be successful.	Theaet. But, Socrates, your question about knowledge I am not likely to answer as readily as that about the geometrical extension and the power of number, though it seems to me that you require some such a reply. I  (p 11)
Socrates compares himself to a midwife. He denies that he puts forth any view at all, but only brings out the philosophical ideas of others. An important political expedient.	Soc. Consider now the whole case of these mid wives, and you will more easily perceive my meaning. You are aware, of course, that none of them while she is herself having a family, acts as midwife to others, but only those who are now too old to have offspring. (p 12)
Socrates continues to compare himself to a midwife/matchmaker/abortionist of ideas. He considers the idea put forth by others and examines them and discarding falsehoods as a midwife discards an unviable fetus.	For I can't tell you that many have shown such a temper towards me as to be quite ready to bite me when I propose to rid them of some nonsensical idea. They fancy that I am not acting kindly in doing this they are yet very far from understanding that, as no god bears any ill will to man, so I do nothing of this sort from unkindness; it is because it is not permitted me to concede falsehood or to put out of sight the truth. (p 15)
2^nd definition Theaetetus introduces the Protagorean theory of appearing.  KNOWLEDGE = PERCEPTION	Knowledge is nothing else than perception. (p 15)
Socrates restates the proposal.	Soc. Indeed, you seem to have delivered an opinion about knowledge that is by no means commonplace: for it is one that Protagoras also gave, though it was in a somewhat different way that he expressed the same meaning. If I mistake not, he says that Man is the measure of all things, of things that are, that they are so, and of non-existing things that they are not. You have read it, I think? (p 15)
An Objection On this theory knowledge appears relative to an observer. But, if the objects of knowledge, e.g. wind are considered properties of the world, then a single object may have inconsistent properties, a logically intolerable result on Socrates’ view. The result is that we cannot distinguish veridical from non-veridical perception. If we accept the Protagorean theory we seem to have no way of accounting for falsehoods about an objective world.	Soc. Does he not then say, in effect, that as things appear severally to me, such they are to me, and as they seem to you, to you they are: and both of us, I suppose, are human beings. . . .   Does it not happen sometimes, when the wind blows, that one of us feels cold, another does not? And one feels it but slightly, another very much? Theaet. Certainly. Soc. Must we then on that particular occasion say that the wind is cold of itself, or not cold? Or must we accept the view of Protagoras, that to the man who shivers it is cold, but him who does not, it is not cold? Theaet. That is probable. Soc. Then it also seems so to each of them? Theaet. Yes. Soc. And this word "seems" is perceives. Theaet. It is so. Soc. Then fancy and perception are the same,  at least in feelings of heat and all sensations of that kind. For just as each person feels them, such, as it seems, they are to each. Theaet. Likely enough. Soc. Then perception must always be of something that exists; and it cannot be mistaken, since it is exact science. Theaet. It seems so. (pp 15 – 16)
The SECRET DOCTRINE : Here is an ontological theory about the nature of the world that incorporates a theory of language and provides the background assumptions against which to analyze the epistemological theory to the effect that knowledge is nothing else but perception.	a truly wise man when he gave us, who are but the rabble multitude, a mere hint of this beautiful doctrine, but told his disciples the whole truth under the seal of secrecy? Theaet. In what sense do you say this, Socrates? Soc. I will tell you a doctrine of no commonplace kind. Nothing exists singly and by itself, and you cannot rightly call anything of itself by any name; but if you speak of it as great, it will seem under other conditions to be small; if heavy, also light; and so with everything else, on the ground of there being no single existence either as a thing or as a quality. The things we now speak of as existing, using thereby an incorrect expression, are really produced from change of position and motion and union of one with another; for nothing ever is; it is ever being produced. On this point all philosophers ranged together, Parmenides excepted, agree; Protagoras following Heraclitus, and Empedocles; as well as the great composers of each kind of poetry, Epicharmus of comedy, Homer of tragedy. For Homer, in saying: "Ocean, from whom the gods were created, and Tethys their mother," has in effect declared that all things are produced from flux and movement. Does he not seem to you to mean this? (pp 16 – 17)
An attempt at physiological description Seeing is defined as an epiphenomenon unique to each perceiver and relative to time, place and condition of change in observer and observed.	Soc. Let us follow our late argument, and assume that nothing exists as a one by itself. Thus black and white and any other colour you please will be found to be produced by the eye being directed to the object with the kind of motion that suits that organ and thus what we call colour of any kind will not be the object that strikes nor the eye that is struck, but an intermediate effect brought into existence for the particular person at the time. Or would you insist that what seems any colour to you, is also the same to a dog or to any creature? (p 18)
The secret doctrine continued. A physics of sight. Note, to keep things from coming to rest,  “seeing-eye“ is introduced as a new linguistic convention. All qualities of sensation follow the same pattern of pair wise interaction producing epiphenomena. Recommends linguistic conventions that prohibit singular nouns and indexicals.	Soc. Then attend, and we will see if we can arrive at a conclusion. The import of the argument is this: that all things with which we are conversant have motion, but in that motion there is sometimes speed and sometimes slowness. Now the slow kind of movement takes place without change of position, and produces its results in this way; [that which has speed,] has a real motion towards the sentient faculties which will admit of a union, and the results so produced are quicker; for they have motion in space, and their movement is naturally one of change in position. Thus, when the eye, and any other object suited to the nature of that organ, unite and produce whiteness, and a perception of whiteness coincident and con genial with it, which never could have resulted, had each of them gone to any other, then, at the moment when the sight from the eyes, and the whiteness from the object which, in contact with the eyes, produces the colour, meet in mid course, the eye becomes filled with sight, and then begins to see, and the result is, not sight but a seeing eye; while the object which, together with the eye, gave birth to the appearance of the colour, is invested with whiteness, and thus here, too, the effect produced is, not whiteness, but a white stick or stone or whatever object it may be, the surface of which happens to be coloured with such a colour. And so it is with all other qualities, we must take the same view of hard and hot and everything else, viz. that, as we before said, nothing has an absolute existence by itself, but that all effects are produced by a relation and intercourse between patient and agent, and varied in their results according to the kind of movement. For to conceive of both an agent and also a patient in any one thing singly, so as to deny motion, is, they tell us, an impossibility. There can be no agent, till it has come into contact with a patient nor a patient, unless it has an agent. And that which, by being in contact with one thing, is an agent, becomes in turn a patient combined with some other thing. So that from all these considerations we must conceive, as I said at first, that no one quality can exist singly and by itself; it only becomes so-and-so to the particular person who perceives it; and absolute existence must be taken away from everything, even though we, partly from familiarity and partly from want of skill, have been compelled to use it for many purposes in our late discussion. We ought not, however, as the philosophers tell us, to concede the existence of anything belonging to me or to anybody else; nor "this" nor "that", nor any other term that tends to fix a thing as constant. We should speak of them according to the true nature of the phenomena, as "brought into being," or "created," or "perishing," or "being altered." For if one adopts any term that fixes existence, he is easily proved to be in the wrong; we ought to use the above expressions both of things severally and of an aggregate of many, such generalizations as they convey by the terms "man," or "stone," or any particular creature or kind of things. Well, Theaetetus, do these doctrines seem nice? Would you like a further taste of them, as of food that you relish? (p 21–22)
The Protagorean theory’s identification of knowledge with perception even augmented with and ontological theory seems to leave out an account of non-veridical perceptions.	Soc. Then don't let us leave off while any part of the argument is incomplete. We have yet to discuss the subject of dreams, and of madness among other diseases, and such fancies as  result from wrong hearing, or wrong seeing, or any other false perception. For you are aware, of course, that in all such cases as these the argument we maintained is allowed to be proved false, since in these states and conditions there assuredly are such things as false perceptions; and so far from each man's fancies being true for himself, absolutely nothing of what seems, really is so to him.(p 23)
The theory summarized.	Soc. Then you put it very well when you said that Know ledge is nothing else than Perception. So it comes to the same thing whether, according to Homer and Heraclitus and all that school, all things are ever in motion, like currents; or, according to Protagoras, that wisest of men, man is the measure of all things; or, according to Theaetetus, these facts being assumed, that Perception comes to be Knowledge. Is it not so, Theaetetus? Must we say this doctrine is a newly-born brat of yours, and that I have been concerned only in the delivery of it? Or how say you?(p28)
Objection The theory seems self-contradictory because it gives no account of expertise.  If each individual’s measure is knowledge, then even a baboon’s measure counts as well.	Soc. . . . . The measure of all things is a Pig or a baboon, or some other still more outlandish specimen of such creatures as are endowed with the faculty for feeling.(p 28-29)
Reply Noting a difficulty with the Protagorean theory is far from producing a counter argument. The model of proof proposed was that of mathematical rigor not probability.	Soc. Ah! you are young, my friend, and therefore your ears and your mind are readily open to the lecture you have heard. (But don't be alarmed); for in reply to this, Protagoras, or someone in his behalf, will say, My fine fellows, men and boys, here you are sitting together and talking fine, and bringing forward the gods, though I expressly exempt them both in speaking and in my writings, and decline to say whether there are or are not such beings. You only say what the mass of mankind would accept if they heard it, that it is strange if human beings, each and severally, shall have no superiority in respect of wisdom over any animal; but as for proof or cogent argument, you adduce none whatever; you adopt a view that is a mere probability, albeit, if Theodore or any other geometer chose to employ it, he would be worth simply nothing. Consider therefore, both you and Theodore, if you are prepared to accept statements made on such weighty matters by mere probabilities and plausible talk. (p 30)
Objection Examples from language learning suggest that knowledge encompasses more than just perception. Note: this does not by itself refute a weaker Protagorean theory of appearing to the effect that some knowledge is perception, but, it does pose a counter example to the Identity of Knowledge and Perception.	Soc. . . . .if we have not learned the dialect of foreigners, are we to say that we don't hear them, when they speak, or that we don't hear them with understanding? So again, if we don't know letters, when we look at them are we to say that we don't see them, or to insist that, of course, if we see them, we understand them? Theaet. Only just this part of them, Socrates, that we actually see and hear, we shall say we understand; that is to say, that we both see and know the shape and colour of the letters, and hear and apprehend the shrill or the deep tones of the voices; but such explanations of the meaning of both as writing-masters or interpreters give, we shall allow that we do not know, as we do not realize them by seeing or hearing. (p 30-31)
Objection If remembered and recalled perceptions count as something known, then we have another counter example to the identity of knowledge and perception since memories do not seem to co-occur with perception.	Soc. Well, now, if a man saw an object, I suppose he remembers it sometimes? Soc. When he shuts his eyes? Or does he forget it when he does that? Soc. But this doesn't see it means doesn't know it , if, as we say, he sees means he knows . Soc. It follows then, that, if a man became acquainted with something, though he still remembers it, he does not know it, since he does not actually see it!
Reply The previous worries about memory are solved by skepticism about personal identity. Note: this is view is to be attributed to an interpretation of Protagoras. The problem of expertise is answered by pointing to persuasion as an agent of change.	Soc: . . . do you imagine anyone will concede to you that, if the memory abides in anyone of something that he underwent, it is a feeling of the same kind as it was when he underwent it, viz. now that he no longer feels it? Or again, do you suppose he will hesitate to admit that thus it is possible for the same man to know and not to know the same thing? Or, should he fear such an admission as that, do you suppose he will allow you to maintain that a person who is undergoing some change is identical with what he was before he began to undergo it? In other words, that a man is the particular person always, and not several, and that by a process of becoming this or that in endless variety, if a becoming unlike should take place in him? for I suppose we must be careful not to catch up each other s words. No! my very fine fellow, he will say, do come to the precise point of my assertion, and prove it wrong if you can. Show that our perceptions are not special and peculiar to each of us, or that, if they are such, not at all the more for that what seems to anyone becomes so to him, and to him only (or say, is so to him, if we may use the verb to be ) to whom it seems. But in talking of swine and baboons, you not only act swinishly yourself, but you persuade your hearers to do the same towards my writings; which is not fair play. For I insist that the truth is as I have stated in my book; that each of us is a measure of what is and what is not; though I allow that there is an enormous difference between one man and another in this very respect, that to one man this seems to be and therefore is, to another that. In this sense I am far from denying that there is such a thing as wisdom or a wise man. On the contrary, I even affirm that this very man is wise, who, by producing a change in another, to whom certain things seem and are bad, makes them seem and be good. (p 35)
The question of knowledge is restated in terms of the role of truth.	Soc. They think, then, that wisdom means a true view, and ignorance means a false opinion(p 30)