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 KantMan's duty is to improve himself; to cultivate his mind; and, when he finds himself going astray, to bring the moral law to bear upon himself.
Immanuel KantThis 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.
Immanuel Kant