The more we come in contact with animals and observe their behaviour, the more we love them, for we see how great is their care of the young.

If we knew that god exists, such knowledge would make morality impossible. For, if we acted morally from fear or fright, or confident of a reward, then this would not be moral. It would be enlightened selfishness.

Man relates to material things through direct insight rather than reason.

Freedom is the alone unoriginated birthright of man, and belongs to him by force of his humanity; and is independence on the will and co-action of every other in so far as this consists with every other person's freedom.

Often war is waged only in order to show valor; thus an inner dignity is ascribed to war itself, and even some philosophers have praised it as an ennoblement of humanity, forgetting the pronouncement of the Greek who said, 'War is an evil in as much as it produces more wicked men than it takes away.'

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.

This can never become popular, and, indeed, has no occasion to be so; for fine-spun arguments in favour of useful truths make just as little impression on the public mind as the equally subtle objections brought against these truths. On the other hand, since both inevitably force themselves on every man who rises to the height of speculation, it becomes the manifest duty of the schools to enter upon a thorough investigation of the rights of speculative reason, and thus to prevent the scandal which metaphysical controversies are sure, sooner or later, to cause even to the masses.