All that I know is nothing - I'm not even sure of that.

I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.

You don't know what you don't know.

No honey is sweeter than that of knowledge.

Every extension of knowledge arises from making the conscious the unconscious.

Partial knowledge is more triumphant than complete knowledge; it takes things to be simpler than they are, and so makes its theory more popular and convincing.