Even those who have desired to work out a completely positive philosophy have been philosophers only to the extent that, at the same time, they have refused the right to install themselves in absolute knowledge. They taught not this knowledge, but its becoming in us, not the absolute but, at most, our absolute relation to it, as Kierkegaard said. What makes a philosopher is the movement which leads back without ceasing from knowledge to ignorance, from ignorance to knowledge, and a kind of rest in this movement.
p. 5 - In Praise of Philosophy (1963)