Here then we see philosophy brought to a critical position, since it has to be firmly fixed, notwithstanding that it has nothing to support it in heaven or earth. Here it must show its purity as absolute director of its own laws, not the herald of those which are whispered to it by an implanted sense or who knows what tutelary nature. Although these may be better than nothing, yet they can never afford principles dictated by reason, which must have their source wholly a priori and thence their commanding authority, expecting everything from the supremacy of the law and due respect for it, nothing from inclination, or else condemning the man to self-contempt and inward abhorrence.

— Immanuel Kant

He who is cruel to animals becomes hard also in his dealings with men. We can judge the heart of a man by his treatment of animals.

— Immanuel Kant

He who would know the world must first manufacture it.

— Immanuel Kant

...[H]human reason in its pure use, so long as it was not critically examined, has first tried all possible wrong ways before it succeeded in finding the one true way.

— Immanuel Kant

High towers, and metaphysically-great men resembling them, round both of which there is commonly much wind, are not for me. My place is the fruitful bathos, the bottom-land, of experience; and the word transcendental, does not signify something passing beyond all experience, but something that indeed precedes it a priori, but that is intended simply to make cognition of experience possible.

— Immanuel Kant

Human beings are never to be treated as a means but always as ends.

— Immanuel Kant

... I am never to act otherwise than so that I could also will that my maxim should become universal law.

— Immanuel Kant

I class the principle of moral feeling under that of happiness, because every empirical interest promises to contribute to our well-being by the agreeableness that a thing affords, whether profit be regarded.

— Immanuel Kant

If adversity and hopeless grief have quite taken away the taste for life; if an unfortunate man, strong of soul and more indignant about his fate than despondent or dejected, wishes for death and yet preserves his life without loving it, not from inclination or fear but from duty, then his maxim has moral content.

— Immanuel Kant

If I have a book that thinks for me, a pastor who acts as my conscience, a physician who prescribes my diet, and so on... then I have no need to exert myself. I have no need to think, if only I can pay; others will take care of that disagreeable business for me.

— Immanuel Kant