G.E. Moore's Open Question Argument and the Naturalistic Fallacy

George Edward Moore's Principia Ethica, published in 1903 at Cambridge, opens with the claim that ethics has been almost universally vitiated by a single confusion: the attempt to define the fundamental ethical term "good" by identifying it with some natural or metaphysical property, such as pleasure, what is desired, or what is willed by God. Moore calls this move the naturalistic fallacy, and although the label has since been criticized as a misnomer — since the fallacy, as Moore describes it, would apply equally to identifying good with a non-natural metaphysical property, such as Plato's Form of the Good, making "naturalistic" a poor label for the general error — the term has become permanently attached to his argument. For Moore, "good" names a property that is simple, unanalyzable, and non-natural: simple in that it has no parts into which it can be conceptually decomposed, unanalyzable in that it cannot be defined in terms of anything else, and non-natural in that it cannot be studied by the natural sciences or metaphysics in the way that yellowness or pleasure can.