Enlightenment is man's emergence from his self-imposed immaturity...No thing is required for this enlightenment.. .except freedom; and the freedom in question is the least harmful of all, namely, the freedom to use reason publicly in all matters.
Act in such a way that you treat humanity, whether in your own person or in the person of any other, never merely as a means to an end, but always at the same time as an end.
Christianity possesses the great advantage over Judaism of being represented as coming from the mouth of the first Teacher not as a statutory but as a moral religion, and as thus entering into the closest relation with reason so that, through reason, it was able of itself, without historical learning, to be spread at all times and among all peoples with the greatest trustworthiness.
The instruction of children should aim gradually to combine knowing and doing. Among all sciences mathematics seems to be the only one of a kind to satisfy this aim most completely.
The infinitude of creation is great enough to make a world, or a Milky Way of worlds, look in comparison with it what a flower or an insect does in comparison with the Earth.
Even if a civil society were to be dissolved by the consent of all its members (e.g., if a people inhabiting an island decided to separate and disperse throughout the world), the last murderer remaining in prison would first have to be executed, so that each has done to him what his deeds deserve and blood guilt does not cling to the people for not having insisted upon this punishment; for otherwise the people can be regarded as collaborators in his public violation of justice.
Marriage...is the union of two people of different sexes with a view to the mutual possession of each other's sexual attributes for the duration of their lives.
The ideal of the supreme being is nothing but a regulative principle of reason which directs us to look upon all connection in the world as if it originated from an all-sufficient necessary cause.
In the metaphysical elements of aesthetics the various nonmoral feelings are to be made use of; in the elements of moral metaphysics the various moral feelings of men, according to the differences in sex, age, education, and government, of races and climates, are to be employed.
No state at war with another state should engage in hostilities of such a kind as to render mutual confidence impossible when peace will have been made.