We can never, even by the strictest examination, get completely behind the secret springs of action. - Immanuel Kant

...Reason should take on anew the most difficult of all its tasks, namely, that of self-knowledge, and to institute a court of justice, by which reason may secure its rightful claims while dismissing all its groundless pretensions, and this not by mere decrees but according to its own eternal and unchangeable laws; and this court is none other than the critique of pure reason itself.

The question here is not, “How conscience ought to be guided? For Conscience is its own General and Leader; it is therefore enough that each man have one. What we want to know is, how conscience can be her own Ariadne, and disentangle herself from the mazes even of the most raveled and complicated casuistical theology. Here is an ethical proposition that stands in need of no proof: No Action May At Any Time Be Hazarded On The Uncertainty That Perchance It May Not Be Wrong (Quod dubitas, ne feceris! Pliny - which you doubt, then neither do) Hence the Consciousness, that Any Action I am about to perform is Right, is in itself a most immediate and imperative duty. What actions are right, - what wrong – is a matter for the understanding, not for conscience. p. 251

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.