The materialists say, it is by means of a series of straight lines more or less perfect that one imagines the perfect straight line as an ideal limit. That is right, but the progression in itself necessarily contains what is infinite; it is in relation to the perfect straight line that one can say that such and such a straight line is less twisted than some other.... Either one conceives the infinite or one does not conceive at all.

p. 87 - Lectures on Philosophy (1959)