This distinction between use and possession saves us from the absurdity of supposing that we do not know what we know, because we may know in one sense, i.e. possess, what we do not know in another, i.e. use. But have we not escaped one difficulty only to encounter a greater? For how can the exchange of two kinds of knowledge ever become false opinion? As well might we suppose that ignorance could make a man know, or that blindness could make him see. Theaetetus suggests that in the aviary there may be flying about mock birds, or forms of ignorance, and we put forth our hands and grasp ignorance, when we are intending to grasp knowledge. But how can he who knows the forms of knowledge and the forms of ignorance imagine one to be the other? Is there some other form of knowledge which distinguishes them? and another, and another? Thus we go round and round in a circle and make no progress. All this confusion arises out of our attempt to explain false opinion without having explained knowledge. What then is knowledge? Theaetetus repeats that knowledge is true opinion. But this seems to be refuted by the instance of orators and judges. For surely the orator cannot convey a true knowledge of crimes at which the judges were not present; he can only persuade them, and the judge may form a true opinion and truly judge. But if true opinion were knowledge they could not have judged without knowledge. Once more. Theaetetus offers a definition which he has heard: Knowledge is true opinion accompanied by definition or explanation. Socrates has had a similar dream, and has further heard that the first elements are names only, and that definition or explanation begins when they are combined; the letters are unknown, the syllables or combinations are known. But this new hypothesis when tested by the letters of the alphabet is found to break down. The first syllable of Socrates' name is SO. But what is SO? Two letters, S and O, a sibilant and a vowel, of which no further explanation can be given. And how can any one be ignorant of either of them, and yet know both of them? There is, however, another alternative:--We may suppose that the syllable has a separate form or idea distinct from the letters or parts. The all of the parts may not be the whole. Theaetetus is very much inclined to adopt this suggestion, but when interrogated by Socrates he is unable to draw any distinction between the whole and all the parts. And if the syllables have no parts, then they are those original elements of which there is no explanation. But how can the syllable be known if the letter remains unknown? In learning to read as children, we are first taught the letters and then the syllables. And in music, the notes, which are the letters, have a much more distinct meaning to us than the combination of them.