He who is cruel to animals becomes hard also in his dealings with men. We can judge the heart of a man by his treatment of animals.

The only thing permanent is change.

All our knowledge begins with the senses...

Physicians think they do a lot for a patient when they give his disease a name.

Life is the faculty of spontaneous activity, the awareness that we have powers.

Thoughts without content are empty, intuitions without concepts are blind... The understanding can intuit nothing, the senses can think nothing. Only through their union can knowledge arise.

Have the courage to use your own reason- That is the motto of enlightenment. "Foundations of the Metaphysics of Morals" (1785)