Hume’s Law

Hume's law, that is, that moral claims cannot be inferred from exclusively nonmoral claims, is widely accepted by recent and contemporary philosophers, some exceptions being John Searle and A. N. Prior. Chapter 1 distinguishes three versions of the law: the formal version ), the conceptual version ), and the epistemic version ), all of which, according to Salwén, are true. When "valid inference" means "a sentence is a logical consequence of a set of sentences K iff there is no interpretation under which all the sentences of K are true and x false", then the law is, HL: "For all valid arguments, K>X, and all moral expressions Ö, if Ö occurs nonvacuously in X, then Ö appears in K". When "valid inference" means an inference "such that the truth of the premise conceptually guarantees the truth of the conclusion", and when a bridge premise is a conditional sentence whose antecedent is a nonmoral sentence and whose consequence is a categorial norm or moral sentence, then the law reads, HL: "There are no analytic bridge sentences". Thus, HL implies, as against Searle, that the bridge premise, "If Jones has promised to pay Smith five dollars, then Jones ought to pay Smith five dollars," is false. Unlike either HL or HL, HL is about nonmoral reasons for holding moral beliefs. Thus, "HL implies that, say, the acceptance of 'Jones has promised to pay Smith five dollars' is a reason to accept 'Jones ought to pay Smith five dollars' only if it is accepted that promises ought to be kept".