One can mistrust one's own senses, but not one's own belief.

The world of those who are happy is different from the world of those who are not.

A philosopher who is not taking part in discussions is like a boxer who never goes into the ring.

The philosopher is not a citizen of any community of ideas, that is what makes him a philosopher.

I am still at Trattenbach, surrounded, as ever, by odiousness and baseness. I know that human beings on the average are not worth much anywhere, but here they are much more good-for-nothing and irresponsible than elsewhere.

Almost in the same way as earlier physicists are said to have found suddenly that they had too little mathematical understanding to be able to master physics; we may say that young people today are suddenly in the position that ordinary common sense no longer suffices to meet the strange demands life makes. Everything has become so intricate that for its mastery an exceptional degree of understanding is required. For it is not enough any longer to be able to play the game well; but the question is again and again: what sort of game is to be played now anyway?

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