Freedom is independence of the compulsory will of another, and in so far as it tends to exist with the freedom of all according to a universal law, it is the one sole original inborn right belonging to every man in virtue of his humanity.
Even the song of birds, which we can bring under no musical rule, seems to have more freedom, and therefore more for taste, than a song of a human being which is produced in accordance with all the rules of music; for we very much sooner weary of the latter, if it is repeated often and at length. Here, however, we probably confuse our participation in the mirth of a little creature that we love, with the beauty of its song; for if this were exactly imitated by man (as sometimes the notes of the nightingale are) it would seem to our ear quite devoid of taste.
The ultimate destiny of the human race is the greatest moral perfection, provided that it is achieved through human freedom, whereby alone man is capable of the greatest happiness.
If you punish a child for being naughty, and reward him for being good, he will do right merely for the sake of the reward; and when he goes out into the world and finds that goodness is not always rewarded, nor wickedness always punished, he will grow into a man who only thinks about how he may get on in the world, and does right or wrong according as he finds advantage to himself.
In the kingdom of ends everything has either a price or a dignity. Whatever has a price can be replaced by something else as its equivalent; on the other hand, whatever is above all price, and therefore admits of no equivalent, has a dignity. But that which constitutes the condition under which alone something can be an end in itself does not have mere relative worth, i.e., price, but an intrinsic worth, i.e., a dignity.
The sum total of all possible knowledge of God is not possible for a human being, not even through a true revelation. But it is one of the worthiest inquiries to see how far our reason can go in the knowledge of God.
[S]uppose the mind of [a] friend of humanity were clouded over with his own grief, extinguishing all sympathetic participation in the fate of others; he still has the resources to be beneficent to those suffering distress, but the distress of others does not touch him because he is sufficiently busy with his own; and now, where no inclination any longer stimulates him to it, he tears himself out of his deadly insensibility and does the action without any inclination, solely from duty.
Enlightenment is man's leaving his self-caused immaturity. Immaturity is the incapacity to use one's intelligence without the guidance of another. Such immaturity is self-caused if it is not caused by lack of intelligence, but by lack of determination and courage to use one's intelligence without being guided by another. Sapere Aude! Have the courage to use your own intelligence! is therefore the motto of the enlightenment.