What Copernicus really achieved was not the discovery of a true theory but of a fertile new point of view.

If I have exhausted the justifications, I have reached bedrock and my spade is turned. Then I am inclined to say: 'This is simply what I do.

He who lives in the present lives in eternity.

A propositional sign, applied and thought out, is a thought. A thought is a proposition with a sense.

If you tried to doubt everything you would not get as far as doubting anything. The game of doubting itself presupposes certainty.

In order to draw a limit to thinking, we should have to think both sides of this limit.

I am not interested in constructing a building, so much as in having a perspicuous view of the foundations of possible buildings.