  In the Treatise Hume’s principle interest in the natural virtues lies in explaining the causes that make us approve them. The mechanism of sympathy ultimately accounts for this approval and the corresponding disapproval of the natural vices. Sympathy also explains our approval of the artificial virtues; the difference is that we approve of those as a result of sympathy with the cumulative effects produced by the general practice of the artificial virtues on the whole of society (individual acts of justice not always producing pleasure for anyone); whereas we approve each individual exercise of such natural virtues as gratitude and friendship because we sympathize with those who are affected by each such action when we consider it from the common point of view. As we saw, he argues that the traits of which we approve fall into four groups: traits immediately agreeable to their possessor or to others, and traits advantageous to their possessor or to others. In these four groups of approved traits, our approval arises as the result of sympathy bringing into our minds the pleasure that the trait produces for its possessor or for others (with one minor exception). This is especially clear with such self-regarding virtues as prudence and industry, which we approve even when they occur in individuals who provide no benefit to us observers; this can only be explained by our sympathy with the benefits that prudence and industry bring to their possessors.