More Bad Newsfor the Logical Autonomy of Ethics

Abstract

Since the time of Hume, many philosophers have thought it impossible to deduce an ‘Ought’ from an ‘Is,’ or in general to deduce ‘ethical sentences’ from purely ‘factual sentences.’ Some of these philosophers claim that this is due, not to any Special feature of ethics, but to a general feature of logic, namely, its conservativeness:A conclusion containing an ‘ought’ cannot (as a matter of logic) be derived from ‘ought’-free premises. (The same, of course, goes for the other moral words.) Logic is conservative; the conclusions of a valid inference are contained within the premises. You don't get out what you haven't put in. Hence if ‘ought’ appears in the conclusion of an argument but not in the premises, the inference is not logically valid.’