Then the wise or temperate man, and he only, will know himself, and be
able to examine what he knows or does not know, and to see what others
know and think that they know and do really know; and what they do not
know, and fancy that they know, when they do not. No other person will
be able to do this. And this is wisdom and temperance and
self-knowledge-for a man to know what he knows, and what he does not
know. That is your meaning?
Yes, he said.
Now then, I said, making an offering of the third or last argument to
Zeus the Saviour, let us begin again, and ask, in the first place,
whether it is or is not possible for a person to know that he knows
and does not know what he knows and does not know; and in the second
place, whether, if perfectly possible, such knowledge is of any use.
That is what we have to consider, he said.
And here, Critias, I said, I hope that you will find a way out of a
difficulty into which I have got myself. Shall I tell you the nature
of the difficulty?
By all means, he replied.
Does not what you have been saying, if true, amount to this: that
there must be a single science which is wholly a science of itself and
of other sciences, and that the same is also the science of the
absence of science?
But consider how monstrous this proposition is, my friend: in any
parallel case, the impossibility will be transparent to you.
How is that? and in what cases do you mean?
In such cases as this: Suppose that there is a kind of vision which is
not like ordinary vision, but a vision of itself and of other sorts of
vision, and of the defect of them, which in seeing sees no colour, but
only itself and other sorts of vision: Do you think that there is such
a kind of vision?
Or is there a kind of hearing which hears no sound at all, but only
itself and other sorts of hearing, or the defects of them?
There is not.
Or take all the senses: can you imagine that there is any sense of
itself and of other senses, but which is incapable of perceiving the
objects of the senses?
I think not.
Could there be any desire which is not the desire of any pleasure, but
of itself, and of all other desires?
Or can you imagine a wish which wishes for no good, but only for
itself and all other wishes?
I should answer, No.
Or would you say that there is a love which is not the love of beauty,
but of itself and of other loves?
I should not.
Or did you ever know of a fear which fears itself or other fears, but
has no object of fear?
I never did, he said.
Or of an opinion which is an opinion of itself and of other opinions,
and which has no opinion on the subjects of opinion in general?
But surely we are assuming a science of this kind, which, having no
subject-matter, is a science of itself and of the other sciences?
Yes, that is what is affirmed.
But how strange is this, if it be indeed true: must not however as yet
absolutely deny the possibility of such a science; let us rather
consider the matter.
You are quite right.
Well then, this science of which we are speaking is a science of
something, and is of a nature to be a science of something?