Principia Ethica by G. E. Moore

24. It results from the conclusions of Chapter I, that all ethical questions fall under one or other of three classes. The first class contains but one question -- the question What is the nature of that peculiar predicate, the relation of which to other things constitutes the object of all other ethical investigations? or, in other words, What is meant by good? This first question I have already attempted to answer. The peculiar predicate, by reference to which the sphere of Ethics must be defined, is simple, unanalysable, indefinable. There remain two classes of questions with regard to the relation of this predicate to other things. We may ask either (1) To what things and in what degree does this predicate directly attach? What things are good in themselves? or (2) By what means shall we be able to make what exists in the world as good as possible? What causal relations hold between what is best in itself and other things?

In this and the two following chapters, I propose to discuss certain theories, which offer us an answer to the question What is good in itself? I say advisedly -- an answer: for these theories are all characterised by the fact that, if true, they would simplify the study of Ethics very much. They all hold that there is only one kind of fact, of which the existence has any value at all. But they all also possess another characteristic, which is my reason for grouping them together and treating them first: namely that the main reason why the single kind of fact they name has been held to define the sole good, is that it has been held to define what is meant by "good" itself. In other words they are all theories of the end or ideal, the adoption of which has been chiefly caused by the commission of what I have called the naturalistic fallacy: they all confuse the first and second of the three possible questions which Ethics can ask.