Synthese 199 (1-2):617-635 (
2020)
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Abstract
Why do we have a moral duty to fulfill promises? Hume offers what today is called a practice theory of the obligation of promises: he explains it by appeal to a social convention. His view has inspired more recent practice theories. All practice theories, including Hume’s, are assumed by contemporary philosophers to have a certain normative structure, in which the obligation to fulfill a promise is warranted or justified by a more fundamental moral purpose that is served by the social practice of promising or adherence to it. Recent practice theories do have this structure, but, I argue, Hume’s own does not. Hume’s account, while it does trace the origin of promises to convention, is instead a causal explanation of the moral sentiments we have toward fulfillment and violation of promises, sentiments he regards as normative in themselves and not susceptible of further warrant. He explains how a collectively-invented social practice becomes morally obligatory for us to conform to, without deriving its moral authority from a more basic principle. I discuss one objection often made to practice theories that, in its application to Hume, presupposes the incorrect interpretation, and show that while it is telling for Hume’s descendants, for Hume it misses the mark. Instead I make a different challenge to Hume, and suggest how he might meet it.