Hume's Law
An Essay on Moral Reasoning

By Hakan Salwen
December 2003
Almqvist & Wiksell International
ISBN: 91-22-02044-6
154 pages, 6" x 9 ½"
$62.50 Paper Original

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Hume's law is a thesis about moral reasoning. It claims that a moral conclusion cannot be validly inferred from non-moral premises. Many philosophers embrace the law, while others think that it is false. Some philosophers believe that Hume's Law has profound significance to hypotheses about the nature of moral commitments as well as to the rationality of morals, while there are some who deny that it has any such significance. In this essay, I address both these questions. Due to the ambiguity of locutions like 'valid inference,' three versions of Hume's law are distinguished.

The first version claims that there are no formally valid arguments with non-moral premises and moral conclusions. This version of the law is shown to be a logical truth. The second version of the law claims that there are no conceptually valid arguments from 'is' to 'ought'. Some influential arguments for and against this version of the law are reviewed. Each of these arguments has problems of its own. However, they have a major problem in common, together with the conceptual version of Hume's law itself, namely that they rely on problematic notions such as 'conceptual implication' and 'analyticity'. A partial explication of analyticity is outlined and defended. It is argued that Hume's Law, when understood in terms of the explication, is true. The third version of Hume's Law is an epistemic thesis. It implies that the acceptance of a non-moral claim is a reason for a person to accept a moral conclusion only if he/she also accepts a moral principle that connects the premise with the conclusion. It is argued that this version of the law gains support from a coherentistic account of epistemic justification.

As for the significance of Hume's Law, while the formal version of Hume's law is found to be irrelevant to meta-ethics, the conceptual version is incompatible with certain important doctrines. The significance of the epistemic version of the law is, lastly, considered.

Philosophy
Stockholm Studies in Philosophy, No. 25

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