many kinds? At any rate there are two principal ones. Think.

THEAETETUS: I will.

STRANGER: I believe that I can see how we shall soonest arrive at the
answer to this question.

THEAETETUS: How?

STRANGER: If we can discover a line which divides ignorance into two
halves. For a division of ignorance into two parts will certainly imply
that the art of instruction is also twofold, answering to the two divisions
of ignorance.

THEAETETUS: Well, and do you see what you are looking for?

STRANGER: I do seem to myself to see one very large and bad sort of
ignorance which is quite separate, and may be weighed in the scale against
all other sorts of ignorance put together.

THEAETETUS: What is it?

STRANGER: When a person supposes that he knows, and does not know; this
appears to be the great source of all the errors of the intellect.

THEAETETUS: True.

STRANGER: And this, if I am not mistaken, is the kind of ignorance which
specially earns the title of stupidity.