All our knowledge begins with the senses...

Human reason has this peculiar fate that in one species of its knowledge it is burdened by questions which, as prescribed by the very nature of reason itself, it is not able to ignore, but which, as transcending all its powers, it is also not able to answer.

The only objects of practical reason are therefore those of good and evil. For by the former is meant an object necessarily desired according to a principle of reason; by the latter one necessarily shunned, also according to a principle of reason.

Philosophy stands in need of a science which shall determine the possibility, principles, and extent of human knowledge à priori.

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.

It is difficult for the isolated individual to work himself out of the immaturity which has become almost natural for him.

Genius is the ability to independently arrive at and understand concepts that would normally have to be taught by another person.