German philosopher and one of the central Enlightenment thinkers
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.
Morality is not the doctrine of how we may make ourselves happy, but how we may make ourselves worthy of happiness.
It is not God's will merely that we should be happy, but that we should make ourselves happy.
What can I know? What ought I to do? What can I hope?
All the interests of my reason, speculative as well as practical, combine in the three following questions: 1. What can I know? 2. What ought I to do? 3. What may I hope?
Intuition and concepts constitute... the elements of all our knowledge, so that neither concepts without an intuition in some way corresponding to them, nor intuition without concepts, can yield knowledge.
I had therefore to remove knowledge, in order to make room for belief.
Two things awe me most, the starry sky above me and the moral law within me.
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.
Act that your principle of action might safely be made a law for the whole world.