Immanuel Kant

A categorical imperative would be one which represented an action as objectively necessary in itself, without reference to any other purpose.

Act that your principle of action might safely be made a law for the whole world.
 

All our knowledge begins with the senses, proceeds then to the understanding, and ends with reason. There is nothing higher than reason.

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?

All thought must, directly or indirectly, by way of certain characters, relate ultimately to intuitions, and therefore, with us, to sensibility, because in no other way can an object be given to us.

Always recognize that human individuals are ends, and do not use them as means to your end.

But although all our knowledge begins with experience, it does not follow that it arises from experience.

By a lie, a man... annihilates his dignity as a man.

Even philosophers will praise war as ennobling mankind, forgetting the Greek who said: 'War is bad in that it begets more evil than it kills.'

Experience without theory is blind, but theory without experience is mere intellectual play.

From such crooked wood as that which man is made of, nothing straight can be fashioned.

Happiness is not an ideal of reason, but of imagination.

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.

I had therefore to remove knowledge, in order to make room for belief.

If man makes himself a worm he must not complain when he is trodden on.

Immaturity is the incapacity to use one's intelligence without the guidance of another.

In law a man is guilty when he violates the rights of others. In ethics he is guilty if he only thinks of doing so.

Ingratitude is the essence of vileness.

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.

It is beyond a doubt that all our knowledge that begins with experience.