It takes physical courage to indulge in wickedness. The "good" are too cowardly to do it.

If there is something to pardon in everything, there is also something to condemn.

A reader is doubly guilty of bad manners against an author when he praises his second book at the expense of his first (or vice versa) and then expects the author to be grateful for what he has done.

It is perhaps just dawning on five or six minds that physics, too, is only an interpretation and exegesis of the world (to suit us, if I may say so!) and not a world-explanation.

In a seriously intended intellectual emancipation a person's mute passions and cravings also hope to find their advantage.

One hears but one does not seek; one takes -- one does not ask who gives; a thought flashes up like lightning, it comes of necessity and unfalteringly formed.

The one seeks a midwife to deliver his thoughts, the other, someone to assist: thus a good conversation comes into being.