The finest and healthiest thing about science is, as in the mountains, the brisk air blowing around in it.--The spiritually delicate (such as artists) shun and slander science owing to this air.

We ought to face our destiny with courage.

You lovers of knowledge! So what have you done out of your love of knowledge up to now? Have you already stolen and murdered so as to know how a thief and a murderer feels?

We often refuse to accept an idea merely because the tone of voice in which it has been expressed is unsympathetic to us.

Pity makes suffering contagious.

Probability but no truth, facility but no freedom--it is owing to these two fruits that the tree of knowledge cannot be confused with the tree of life.

Be careful when you fight the monsters, lest you become one.