' ought ' . ethical concepts . ' Is

Moral philosophy in the English-speaking world has been dominated during the present century by the controversy concerning the logical relationship between 'is' and 'ought'. These terms are, of course, to be understood in the present context as shorthand labels. By 'is' is meant any non-moral assertion, that is to say, any utterance which purports to be either true or false and which does not express a moral judgment. By 'ought' is meant any proposition expressing a moral judgment. The question which is at the centre of the controversy may be stated then as follows: Is it possible for a proposition expressing a moral judgment to be deduced from a proposition or set of propositions which do not express moral judgments? The answer would appear to be No, for it is a principle of logic that the conclusion of a valid deductive argument cannot assert something which is not at least implicitly asserted in the premises. Hence, if the conclusion of a deductive argument expresses a moral judgment and the premises do not, it follows that the argument must be invalid.