For these reasons I think there are serious objections to the view that the idea of moral obligation is merely a psychological idea.
But now let us briefly consider the idea of "good," in Aristotle's sense, or intrinsic value.
As regards this idea, there is again a difference of opinion among those who hold that it is a psychological idea, as to _what_ idea it is. The majority seem to hold that it is to be defined, somehow, in terms of desire; while others have held that what we are judging when we judge that one state of things is or would be intrinsically better than another, is rather that the belief that the one was going to be realized would, under certain circumstances, give more pleasure to some man or set of men, than the belief that the other was. But the same objections seem to me to apply whichever of these two views be taken.
Let us take desire. About whose desires am I making a judgment, when I judge that one state of things would be better than another?
Here again, it may be said, first of all, that I am merely making a judgment about my own. But in this case the view that my judgment is merely about my own psychology is, I think, exposed to an obvious objection to which Westermarck's view that my judgments of moral obligation are about my own psychology was not exposed. The obvious objection is that it is evidently not true that I do in fact always desire more, what I judge to be better: I may judge one state of things to be better than another, even when I know perfectly well not only that I don't desire it more, but that I have no tendency to do so. It is a notorious fact that men's strongest desires are, as a rule, for things in which they themselves have some personal concern; and yet the fact that this is so, and that they know it to be so, does not prevent them from judging that changes, which would not affect them personally, would constitute a very much greater improvement in the world's condition, than changes which would. For this reason alone the view that when I judge one state of things to be better than another I am merely making a judgment about my own psychology, must, I think, be given up: it is incredible that we should all be making such mistakes about our feelings, as, on this view, we should constantly be doing. And there is, of course, besides, the same objection, as applied in the case of moral obligation: namely that, if this view were true, no two men could ever differ in opinion as to which of two states was the better, whereas it appears that they certainly sometimes do differ in opinion on such an issue.