When, therefore, I say that the idea of "moral obligation" is one of the fundamental ideas with which Moral Philosophy is concerned, I think we must admit that this one name really stands for two different ideas. But it does not matter for my purpose which of the two you take. Each of them is undoubtedly a moral idea, and whatever answer be given to the question we are going to raise about the one, will also certainly apply to the other.
But it is now time to turn to the other idea, with which I said that Moral Philosophy has been largely concerned, though it is not, strictly speaking, a moral idea, at all.
And I think, perhaps, a good way of bringing out what this idea is, is to refer to the Ethics of Aristotle. Everybody would admit that the fundamental idea, with which Aristotle's Ethics is concerned, is an idea which it is the business of Moral Philosophy to discuss; and yet I think it is quite plain that this idea is not a moral idea at all. Aristotle does not set out from' the idea of moral obligation or duty (indeed throughout his treatise he only mentions this idea quite incidentally); nor even from the idea of moral goodness or moral excellence, though he has a good deal more to say about that; but from the idea of what he calls "the human good," or "good for man." He starts by raising the question what the good for man _is,_ and his whole book is arranged in the form of giving a detailed answer to that question. And I think we can gather pretty well what the idea is, which he calls by this name, by considering what he says about it. There are two points, in particular, which he insists upon from the outset: first, that nothing can be good, in the sense he means, unless it is something which is worth having for its own sake, and not merely for the sake of something else; it must be good _in itself_; it must not, like wealth (to use one example which he gives) be worth having merely for the sake of what you can do with it; it must be a thing which is worth having even if nothing further comes of it. And secondly (what partly covers the former, but also, I think, says something more) it must, he says, be something that is "self-sufficient": something which, even if you had nothing else would make your life worth having. And further light is thrown upon his meaning when he comes to tell you what he thinks the good for man is: the good, he says, is "mental, activity--where such activity is of an excellent kind, or, if there are several different kinds of excellent mental activity, that which has the best and most perfect kind of excellence; and also" (he significantly adds) "mental activity which lasts through a sufficiently long life." The word which I have here translated "excellence" is what is commonly translated "virtue"; but it does not mean quite the same as we mean by "virtue," and that in a very important respect. "Virtue" has come to mean exclusively _moral_ excellence; and if that were all Aristotle meant, you might think that what he means by "good" came very near being a moral idea. But it turns out that he includes among "excellences," intellectual excellence, and even that he thinks that the best and most perfect excellence of which he speaks is a particular kind of intellectual excellence, which no one would think of calling a moral quality, namely, the sort of excellence which makes a man a good philosopher. And as for the word which I have translated "activity," the meaning of this can be best brought out by mentioning the reason which Aristotle himself gives for saying that mere excellence itself is not (as some of the Greeks had said) the good for man. He says, truly enough, that a man may possess the greatest excellence--he may be a very excellent man--even when he is asleep, or is doing nothing; and he points out that the possession of excellence when you are asleep is not a thing that is desirable _for its own sake_--obviously only for the sake of the effects it may produce when you wake up. It is not therefore, he thinks, mere mental excellence, but the _active exercise_ of mental excellence--the state of a man's mind, when he not only possesses excellent faculties, moral or intellectual, but is actively engaged in using them, which really constitutes the human good.