On the other hand, effective social interest is based upon what is vaguely called 'faith in humanity', or, more specifically, belief in the value of each man's individuality, belief in some particular function which he might exercise, given appropriate conditions and stimuli. Moral interest in others must be an interest in their possibilities, rather than in their accomplishments; or, better, in their accomplishments so far as these testify to a fulfilling of function--to a working out of capacity. Sympathy and work for men which do not grow out of faith in them are a perfunctory and unfertile sort of thing.
This faith is generally analyzed no further; it is left as faith in one's 'calling' or in 'humanity'. But what is meant is just this: in the performing of such special service as each is capable of, there is to be found not only the satisfaction of self, but also the satisfaction of the entire moral order, the furthering of the community in which one lives. All moral conduct is based upon such a faith; and _moral theory must recognize this as the postulate upon which it rests_. In calling it a postulate, we do not mean that it is a postulate which our theory makes or must make in order to be a theory; but that, through analysis, theory _finds that moral practice makes this postulate_, and that with its reality the reality end value of conduct are bound up.
In calling it a postulate we do not mean to call it unprovable, much less unverifiable, for moral experience is itself, so far as it goes, its verification. But we mean that the further consideration of this postulate, its demonstration or (if the case so be) its refutation, do not belong to the realm of ethics as such. Each branch of human experience rests upon some presupposition which, _for that branch_, is ultimate. The further inquiry into such presuppositions belong not to mathematics, or physics, or ethics, but to metaphysics.
Unless, then, we are to extend our ethical theory to inquire into the possibility and value of moral experience, unless, that is, we are to make an excursion into the metaphysics of ethics, we have here reached our foundation. The ethical postulate, the presupposition involved in conduct, is this: