A person who already displays … cruelty to animals is also no less hardened towards men. We can already know the human heart, even in regard to anima… - Immanuel Kant

It is discipline, which prevents man from being turned aside by his animal impulses from humanity, his appointed end.

Chisels and hammers may suffice to work a piece of wood, but for etching we require an etcher's needle. Thus common sense and speculative understanding are both useful, but each in its own way: the former in judgments which apply immediately to experience; the latter when we judge universally from mere concepts, as in metaphysics, where sound common sense, so called in spite of the inappropriateness of the word, has no right to judge at all.

Morality is not properly the doctrine of how we may make ourselves happy, but how we may make ourselves worthy of happiness.