Not he is great who can alter matter, but he who can alter my state of mind.

In order to acquire intellect one must need it. One loses it when it is no longer necessary.

Whoever has overthrown an existing law of custom has always first been accounted a bad man: but when, as did happen, the law could not afterwards be reinstated and this fact was accepted, the predicate gradually changed; - history treats almost exclusively of these bad men who subsequently became good men!

Here is a hero who did nothing but shake the tree as soon as the fruit was ripe. Does this seem to be too small a thing to you? Then take a good look at the tree he shook.

Mankind must work continually to produce individual great human beings - this and nothing else is the task... for the question is this : How can your life, the individual life, retain the highest value, the deepest significance? Only by living for the good of the rarest and most valuable specimens.

He who does not desire much more from things than knowledge of them easily makes peace with his soul.

The snake which cannot cast its skin has to die.