Immanuel Kant

We can know only appearances, not things in themselves.

The highest good is virtue combined with happiness.

A categorical imperative is an imperative that commands a certain conduct immediately, without having as its condition any other purpose to be attained by it.

To be truthful (honest) in all declarations is therefore a sacred unconditional command of reason, and not to be limited by any expediency.

The citizen must be assumed to be of full age, and therefore capable of judging for himself what is good or bad for him.

The understanding makes nature, but does not create it.

The highest principle of morality is therefore: Act according to a maxim which can at the same time be valid as a universal law.

Peace is not a state of nature, but a state of society.

The civil constitution in every state shall be republican.

The law of nations shall be founded on a federation of free states.

Cosmopolitan right shall be limited to conditions of universal hospitality.

All political theories, if they are to be consistent, must proceed from the principle that man is a free and rational being.

The greatest good for man is to do his duty.

The moral law is holy.

The will is a kind of causality of living beings insofar as they are rational.

Freedom is the property of the will to be a law to itself.

Autonomy of the will is the supreme principle of morality.

Heteronomy of the will, on the other hand, is the source of all spurious principles of morality.

A lie is an abandonment of human dignity.

The greatest good is the moral law itself.