THEAET. The numbers between these, such as three

 
	
and five and all numbers which cannot be formed by multiplying equal factors, but only by multiplying a greater by a less or a less by a greater, and are therefore always contained in unequal sides, we represented by the shape of the oblong rectangle and called oblong numbers. SOC. Very good; and what next? THEAET. All the lines which form the four sides of the equilateral or square numbers we called lengths, and those which form the oblong numbers we called surds, because they are not commensurable with the others
 
in length, but only in the areas of the planes which they have the power to form. And similarly in the case of solids. That is, cubes and cube roots. SOC. Most excellent, my boys! I think Theodorus will not be found liable to an action for false witness. THEAET. But really, Socrates, I cannot answer that question of yours about knowledge, as we answered the question about length and square roots. And yet you seem to me to want something of that kind. So Theodorus appears to be a false witness after all. SOC. Nonsense! If he were praising your running and said he had never met any young man who was so good a runner, and then you were beaten in a race by a full grown man who held the record, do you think his praise would be any less truthful? THEAET. Why, no. SOC. And do you think that the discovery of knowledge, as I was just now saying, is a small matter and not a task for the very ablest men? THEAET. By Zeus, I think it is a task for the very ablest. SOC. Then you must have confidence in yourself, and believe that Theodorus is right,
 
and try earnestly in every way to gain an understanding of the nature of knowledge as well as of other things. THEAET. If it is a question of earnestness, Socrates, the truth will come to light. SOC. Well then—for you pointed out the way admirably just now—take your answer about the roots as a model, and just as you embraced them all in one class, though they were many, try to designate the many forms of knowledge by one definition. THEAET. But I assure you, Socrates, I have often tried to work that out, when I heard reports of the questions that you asked, but I can neither persuade myself that I have any satisfactory answer, nor can I find anyone else who gives the kind of answer you insist upon; and yet, on the other hand, I cannot get rid of a feeling of concern about the matter. SOC. Yes, you are suffering the pangs of labor, Theaetetus, because you are not empty, but pregnant. THEAET. I do not know, Socrates; I merely tell you what I feel.