The theory of ethics offered by Hume in his Treatise of Human Nature is substantially different from other such theories of the time. In particular, (1) Hume largely attempts to present a descriptive, not normative, account of morality; (2) Hume is concerned not directly with the morality of actions, but with virtuous character; and (3) Hume rejects the idea that reason, so championed by other modern philosophers, plays the primary role in determining the moral worth of actions. On all three counts it can be argued that Hume's moral system does not provide us with a way to evaluate actions and arrive at correct moral decisions. However, I believe this is incorrect. In this paper I will focus on these three observations and sketch replies to several arguments. I hope to show not only that the objections fail and that Humean morality is prescriptive, but also that Hume provides what is in many ways a much richer and more accurate account of ethics than those offered by moral rationalists.
One of Hume's tasks in the Treatise is to describe, not prescribe, morality. The concepts of the passions, virtue, and sympathy are central to an understanding of his moral theory. According to Hume, the passions (emotions) are secondary impressions or impressions of reflection (Hume, 184.108.40.206). These include calm passions such as beauty and deformity, direct violent passion such as grief and joy, and indirect violent passions such as love and hatred. Other passions include generosity, hope, ambition, envy, fear, and despair (Hume, 220.127.116.11). Passions are caused, in part, by virtues and vices, which produce moral pleasures and pains respectively (Hume, 18.104.22.168). In Book 3 Hume explores natural virtues (essential to human nature) such as compassion and friendship, and artificial virtues (social conventions) such as justice, promise-keeping, and allegiance (Hume, 22.214.171.124). Hume's sympathy (rather like empathy) is the means of communication through which we come to understand the sentiments (pains and pleasures) of others and from which we can determine vice and virtue (Hume, 126.96.36.199).
It is the artificial virtues, and in particular justice and promise-keeping, that most concern Hume's description of society. Though these virtues are not natural in the sense of being essential, they arise naturally in society. Society arises out of enlightened self-interest; in particular, Hume says, it is advantageous to join forces to gain power, to form a division of labor to increase ability, and to increase security through mutual succor (Hume, 188.8.131.52). Justice derives its origin from self-interest - ``the selfishness and confin'd generosity of man'' (Hume, 184.108.40.206) - and is maintained by use of sympathy (Hume, 220.127.116.11). Hume illustrates that promise-keeping as well derives from mutual self-interest (Hume, 18.104.22.168). It is the combination of natural self-interest and a sense of an extended societal self that Hume uses to explain the origin and continuation of society, justice, and morality.
Having given an overview of Hume's descriptive account, I turn to a brief consideration of virtue theory. Hume provides neither a consequentialist nor deontic theory and relies instead on virtue. An action is virtuous if it proceeds from a virtuous motive (Hume, 22.214.171.124). A virtuous character, then, is important because virtue motivates moral action. According to Hume's virtue ethics, the moral worth of an action is derived from the virtue with which it was performed. It is important to note that virtuous character both arises naturally and is encouraged by experience and moral education.
Finally, I wish to consider the statement that Hume stands in opposition to moral rationalism. Hume believes that ``[r]eason is, and ought only to be, the slave of the passions'' (Hume, 126.96.36.199). According to Hume, reason alone cannot produce action, so rational judgment plays at most a limited role in moral decision-making (Hume, 188.8.131.52). Yet there is something that motivates the will to moral action, and it is not reason (Hume, 184.108.40.206); it is feelings and passions. Moral sentiments are not logical statements, but expressions of feeling. Here Hume endorses a form of expressivism: morality is not judged, but felt (Hume, 220.127.116.11). To pronounce an action virtuous or vicious is to experience a feeling of praise or blame from the contemplation of the action (Hume, 18.104.22.168).
Does Hume provide a moral framework that can serve as a guide to correct moral action? Recall the first objection that Hume is merely describing a moral system. As Hume provides no way to get from is statements to ought statements, Hume cannot prescribe action. I believe that this objection misses the importance of Hume's work. Moral action and expression of moral sentiments are not rarities in society, but common occurrences. To understand morality, it is necessary to understand both what moral action involves and the role morality plays in society.
A second objection is that without the intervention of reason, we will be unable to deliberate about moral actions and will fail to act morally on many occasions. This, too, I believe, is wrong, as it disregards the fact that we are basically moral and that moral motivation appears to be internal. We do not constantly appeal to reason to determine moral worth; if we are to speak of a faculty of moral sense, it is something quite different from reason. One might further object to Hume's virtue theory that as moral action follows from virtuous character, it leaves those who are not naturally virtuous with no way to perform virtuous or moral actions. Similarly, moral rationalists, seeming to assume that people are not basically moral, insist that reason is required to perform action. These objections fail both because we naturally perform moral action (out of both self-interest and sympathy) and because virtue can be perfected through education. Hume does not leave us without a program for performing moral action; on the contrary, he provides us with explicit guidelines: cultivate a virtuous character and moral action will follow.
Finally, another objection is that it is unclear how Hume makes the leap from virtuous character to virtuous or moral action. How is it that a virtuous person is directed (with little or no conscious intervention) to recognize and perform moral action? Hume addresses this in his very description of the origin and continuance of society. In very small groups the natural virtues alone may lead to moral action, but in larger groups the artificial virtues are required. From sympathy - our ability to share pain and pleasure and observe vice and virtue in the action of others - desire for the artificial virtues naturally arises, and these are the very virtues which will lead to moral action in society.
By Hume's account, performing morally worthy acts is not a matter of calculated, rational deliberation; it follows from human nature. I believe this is preferable to a theory in which morality can only be arrived at through conscious and impersonal reasoning. Furthermore, I believe that Hume is right to reject moral rationalism. When compared with other (perhaps more explicitly prescriptive) theories, Hume's account of moral sentiments provides a more accurate description and explanation of morality. Finally, although Hume does not offer an explicit calculus of moral action, I believe Hume provides a framework for moral action which is prescriptive enough: namely, that the development of virtues leads to moral action.