Abstract
The question of “why be moral?” has been the leading problem in every moral philosophy since Socrates. Hume tackles this problem in the concluding chapter of An Enquiry concerning the Principle of Morals. Many commentators take it that Hume does not commit himself deeply to refuting the “sensible knave,” who is always seeking to commit injustice for personal gain while pretending to be a moral person. I maintain, however, that it is possible to read a fully convincing response to this problem into Hume's theory. The significance of this problem to Hume is, more than anything, its connection to the fierce controversy of Hume's time between the moral sense theories and the egoist moral theories exemplified by Hobbes and Mandeville.
Hume presents mainly two grounds to deny the claim of the “sensible knave.” One is that he is unlikely to successfully follow through with his wicked plan because his wisdom fails to bear up to public scrutiny, and the second is that if he is successful in his injust action, by exchanging the most precious treasure, that is reflection on his own character, for the worthless rubbish that he mistakes for his private interest, he is decisively defeated. I clarify that Hume's claim must be understood based on his comprehensive theory of custom. As moral individuals, we are dependent on the general perception of natural, psychological and moral things, a perception which can be mutually understood among members of a stable community. Moral perceptions also rely on the same psychological mechanism of human nature. Our human nature exerts the same binding force on moral perceptions as natural perceptions do. In this way, I seek to show that Hume's entire theory of the Treatise provides a naturalistic foundation for morality which culminates in the authority of government.
