Enlightenment is man's emergence from his self-incurred immaturity.

Criticism alone can sever the root of materialism, fatalism, atheism, free-thinking, fanaticism, and superstition, which can be injurious universally; as well as of idealism and skepticism, which are dangerous chiefly to the Schools, and hardly allow of being handed on to the public.

When a thoughtful human being has overcome incentives to vice and is aware of having done his bitter duty, he finds himself in a state that could be called happiness, a state of contentment and peace of mind in which virtue is its own reward.

He who has made great moral progress ceases to pray

What can I know? What ought I to do? What may I hope?

[Aristotle formal logic thus far (1787)] has not been able to advance a single step, and hence is to all appearances closed and completed.

Even a man's exact imitation of the song of the nightingale displeases us when we discover that it is a mimicry, and not the nightingale.