Plato Charmides 166

For tell me, he said, what result is there of the arts of reckoning and geometry, in the way that a house is of building, or a coat of weaving, or other products of the sort that one might point to 166a in various arts? Well, can you, for your part, point to any such product in those two cases? You cannot.
  To this I replied: What you say is true; but I can point out to you what is the peculiar subject of each of these sciences, distinct in each case from the science itself. Thus reckoning, I suppose, is concerned with the even and the odd in their numerical relations to themselves and to one another, is it not?
  Certainly, he said.
  And you grant that the odd and the even are different from the actual art of reckoning?
  Of course. 166b And once more, weighing is concerned with the heavier and the lighter weight; but the heavy and the light are different from the actual art of weighing: you agree?
  I do.
  Then tell me, what is that of which temperance is the science, differing from temperance itself?
  There you are, Socrates, he said: you push your investigation up to the real question at issue—in what temperance differs from all the other sciences—but you then proceed to seek some resemblance between it 166c and them; whereas there is no such thing, for while all the rest of the sciences have something other than themselves as their subject, this one alone is a science of the other sciences and of its own self. And of this you are far from being unconscious, since in fact, as I believe, you are doing the very thing you denied you were doing just now: for you are attempting to refute me, without troubling to follow the subject of our discussion.
  How can you think, I said, if my main effort is to refute you, that I do it with any other motive than that which 166d would impel me to investigate the meaning of my own words—from a fear of carelessly supposing, at any moment, that I knew something while I knew it not? And so it is now: that is what I am doing, I tell you. I am examining the argument mainly for my own sake, but also, perhaps, for that of my other intimates. Or do you not think it is for the common good, almost, of all men, that the truth about everything there is should be discovered?
  Yes indeed, he replied, I do, Socrates.
  Then take heart, I said, my admirable friend, and answer the question put to you as you deem the case to be, without caring a jot 166e whether it is Critias or Socrates who is being refuted: give the argument itself your attention, and observe what will become of it under the test of refutation.
  Well, he said, I will do so; for I think there is a good deal in what you say.
  Then tell me, I said, what you mean in regard to temperance.
  Why, I mean, he said, that it alone of all the sciences is the science both of itself and of the other sciences.
  So then, I said, it will be the science of the lack of science also, besides being the science of science? ¹
  Certainly, he replied.