SOCRATES: Let us take them and put them to the test, or rather, test ourselves:--What was the way in which we learned letters? and, first of all, are we right in saying that syllables have a definition, but that letters have no definition? THEAETETUS: I think so. SOCRATES: I think so too; for, suppose that some one asks you to spell the first syllable of my name:--Theaetetus, he says, what is SO? THEAETETUS: I should reply S and O. SOCRATES: That is the definition which you would give of the syllable? THEAETETUS: I should. SOCRATES: I wish that you would give me a similar definition of the S. THEAETETUS: But how can any one, Socrates, tell the elements of an element? I can only reply, that S is a consonant, a mere noise, as of the tongue hissing; B, and most other letters, again, are neither vowel-sounds nor noises. Thus letters may be most truly said to be undefined; for even the most distinct of them, which are the seven vowels, have a sound only, but no definition at all. SOCRATES: Then, I suppose, my friend, that we have been so far right in our idea about knowledge? THEAETETUS: Yes; I think that we have. SOCRATES: Well, but have we been right in maintaining that the syllables can be known, but not the letters? THEAETETUS: I think so. SOCRATES: And do we mean by a syllable two letters, or if there are more, all of them, or a single idea which arises out of the combination of them? THEAETETUS: I should say that we mean all the letters. SOCRATES: Take the case of the two letters S and O, which form the first syllable of my own name; must not he who knows the syllable, know both of them? THEAETETUS: Certainly. SOCRATES: He knows, that is, the S and O? THEAETETUS: Yes. SOCRATES: But can he be ignorant of either singly and yet know both together? THEAETETUS: Such a supposition, Socrates, is monstrous and unmeaning. SOCRATES: But if he cannot know both without knowing each, then if he is ever to know the syllable, he must know the letters first; and thus the fine theory has again taken wings and departed. THEAETETUS: Yes, with wonderful celerity. SOCRATES: Yes, we did not keep watch properly. Perhaps we ought to have maintained that a syllable is not the letters, but rather one single idea framed out of them, having a separate form distinct from them. THEAETETUS: Very true; and a more likely notion than the other. SOCRATES: Take care; let us not be cowards and betray a great and imposing theory. THEAETETUS: No, indeed. SOCRATES: Let us assume then, as we now say, that the syllable is a simple form arising out of the several combinations of harmonious elements--of letters or of any other elements. THEAETETUS: Very good. SOCRATES: And it must have no parts. THEAETETUS: Why? SOCRATES: Because that which has parts must be a whole of all the parts. Or would you say that a whole, although formed out of the parts, is a single notion different from all the parts? THEAETETUS: I should.