s, and
in another he has none of them. Let this aviary be an image of the mind,
as the waxen block was; when we are young, the aviary is empty; after
a time the birds are put in; for under this figure we may describe
different forms of knowledge;--there are some of them in groups, and
some single, which are flying about everywhere; and let us suppose
a hunt after the science of odd and even, or some other science. The
possession of the birds is clearly not the same as the having them in
the hand. And the original chase of them is not the same as taking them
in the hand when they are already caged.

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 b