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.