I should like, if I can, to interest you to-night in one particular question about Moral Philosophy. It is a question which resembles most philosophical questions, in respect of the fact that philosophers are by no means agreed as to what is the right answer to it: some seem to be very strongly convinced that one answer is correct, while others are equally strongly convinced of the opposite. For my own part I do feel some doubt as to which answer is the right one, although, as you will see, I incline rather strongly to one of the two alternatives. I should like very much, if I could, to find some considerations which seemed to me absolutely convincing on the one side or the other; for the question seems to me in itself to be an exceedingly interesting one. I have said that the question is a question _about_ Moral Philosophy; and it seems to me in fact to be a very large and general question which affects the whole of Moral Philosophy. In asking it, we are doing no less than asking what it is that people are doing when they study Moral Philosophy at all: we are asking what sort of questions it is which it is the business of Moral Philosophy to discuss and try to find the right answer to. But I intend, for the sake of simplicity, to confine myself to asking it in two particular instances. Moral Philosophy has, in fact, to discuss a good many different ideas; and though I think this same question may be raised with regard to them all, I intend to pick out two, which seem to me particularly fundamental, and to ask it with regard to them only. My first business must be to explain what these two ideas are.