To think is easy. To act is difficult. To act as one thinks is the most difficult.

All the knowledge I possess everyone else can acquire, but my heart is all my own.

The world of empirical morality consists for the most part of nothing but ill will and envy.

One must be something to be able to do something.

There is no crime of which I do not deem myself capable.

Without my attempts in natural science, I should never have learned to know mankind such as it is. In nothing else can we so closely approach pure contemplation and thought, so closely observe the errors of the senses and of the understanding, the weak and strong points of character.

To have a positive religion is not necessary. To be in harmony with yourself and the universe is what counts, and this is possible without positive and specific formulation in words.