It will at once be objected that this account of moral good either tells us nothing at all about it, or only tells us anything in virtue of some assumption in regard to moral good involved in our notion of a moral agent. The objection is in a certain sense a valid one. The question, What is our moral nature or capability?—in other words, What do we mean by calling ourselves moral agents?—is one to which a final answer cannot be given without an answer to the question, What is moral good? For the moral good is the realisation of the moral capability, and we cannot fully know what any capability is till we know its ultimate realisation. It may be argued therefore that we either know what the moral good in this sense is, and accordingly have no need to infer what it is from our moral nature, or else we do not know what it is, in which case neither can we know that the moral nature is from which we profess to infer what the moral good is. (§172 ¶1)

THe answer is that from a moral capability which had not realised itself at all nothing could indeed be inferred as to the moral good which can only consist in its full realisation; but that the moral capability of man is not in this wholly undeveloped state. To a certain extent it has shown by actual achievement what it has in it to become, and by reflection on the so far developed activity we can form at least some negative conclusion in regard to its complete realisation. We may convince ourselves that this realisation can only be attained in certain directions of our activity, not in others. We cannot indeed describe any state in which man, having become all that he is capable of becoming—all that, according to the divine plan of the world, he is destined to become—would find rest for his soul. We cannot conceive it under any forms borrowed from our actual experience, for our only experience of activity is of such as implies incompleteness. Of a life of completed development, of activity with the end attained, we can only speak or think in negatives, and thus only can we speak or think of that state of being in which, according to our theory, the ultimate moral good must consist. Yet the conviction that there must be such a state of being, merely negative as is our theoretical apprehension of it, may have supreme influence over our conduct, in moving us to htat effort after the Better which, at least as a conscious effort, implies the conviction of there being a Best. (§172 ¶2)

And when the speculative question is raised as to what this Best can be, we find that it has not left itself without witness. The practical struggle after the Better, of which the idea of there being a Best has been the spring, has taken such effort in the world of man’s affairs as makes the way by which the Best is to be more nearly approached plain enough to him that will see. In the broad result it is not hard to understand how man has bettered himself through institutions and habits which tend to make the welfare of all the welfare of each, and through the arts which make nature, both as used and as contemplated, the friend of man. And just so far as this is plain, we know enough of ultimate moral good to guide our conduct: enough to judge whether the prevailing interests which make our character are or are not in the direction which tends further to realise the capabilities of the human spirit. (§172 ¶3)