Hume's Knave and the Interests of Justice

Hume's account of the artificial virtues of justice and promise-keeping developed in Book III, Part ii of the Treatise is among the most provocative elements of his ethics. His goal there is to tell a naturalistic story of the origin and moral standing of these virtues, a story that makes no appeal to any irreducibly moral motives or properties but instead grounds even our most basic and apparently binding obligations in the same thoroughly human passions and sentiments with which Hume explains all our actions. Several modern critics, including David Gauthier and Stephen Darwall, have claimed that Hume's story of the artificial virtues is inconsistent with his account of natural human motivations, and have further claimed that Hume himself became aware of this problem in the second Enquiry, where he discussed it in the famous "sensible knave" passage in the last paragraphs of the "Conclusion." They therefore claim that Hume abandoned in the Enquiry what is usually taken to be his official Treatise account of justice and promise-keeping, and may also have intended a different account in the Treatise itself.

This paper argues that the sensible knave passage neither signals nor requires any significant change in Hume's official Treatise story of the artificial virtues. Part 1 summarizes this official account, Part 2 explains the challenge Gauthier and Darwall believe the sensible knave poses to this account, and Part 3 defends the standard Humean account from this challenge. Whatever other problems Hume's account of justice and promise-keeping may have, the free rider problem, as developed by Gauthier and Darwall through the character of the sensible knave, is not among them.

1. The Interest Account of Artificial Virtues

1.1 Hume's Predecessor Traditions

Hume makes few explicit references to the English-speaking predecessors whose work informs his thinking about the artificial virtues, and I shall follow his example. But without pretending to survey that rich and varied history, we may usefully think of Hume's approach to justice and its allied virtues as an attempt to preserve the strengths of two opposed predecessor traditions.¹ The first tradition, represented most prominently by Hobbes but also by Mandeville, explains the origin of virtues generally, including Humean artificial virtues, in purely naturalistic terms, without any appeal to divinely ordained ends or observer-independent moral facts. Hume shares this humanistic aspiration, but he disavows the cynical skepticism and crude egoism which are usually taken to accompany it. He wants to tell a story about justice which will allow us to admire its genuine moral worth even as we acknowledge its human pedigree.

The second tradition, a reaction to the first, is the moral sense school represented by Shaftesbury, Butler, and especially Hutcheson. This tradition insists, against the cynical egoists, on a moral reality to which our sentiments or consciences give us immediate access, an access secured by God's design. Also characteristic of the moral sense theorists is the claim that human nature contains benevolent motives which are the objects of the moral sense's approval and which are just as basic to our constitution as are selfish motives. Hume avails himself of both moral sense strands, albeit in attenuated form. He agrees that justice and injustice are known by the sentiments, and he also believes that benevolent first-order motives are a part of human nature. But Hume rejects the moral sense tradition's Christian teleology, and he is also less optimistic about the potential of benevolence to explain such complex moral behaviors as are involved in our institutions of justice and promise-keeping.

Hume's standard Treatise story of the origin of justice and promise-keeping, which we may call the "interest account," has two stages. In the first stage, Hume explains how the practices which constitute justice and promise-keeping arise through the working of our natural interests; in this stage Hume might be seen as working in the broadly naturalistic-egoist tradition. In the second stage, Hume explains how these practices and the motives which underlie them become the objects of moral evaluation, i.e., why...