draw on human artifice (his system will include both natural virtues and artificial virtues), adding that none of these meanings can sustain the popular view (defended by Butler) that "virtue is the same with what is natural, and vice with what is unnatural". Before proceeding to his detailed examination of moral psychology, Hume takes a parting shot at moral rationalism and its "incomprehensible relations and qualities, which never did exist in nature, nor even in our imagination, by any clear and distinct conception". Part 2: Of justice and injustice Sections 1–2 Hume devotes Part 2 to the "artificial virtues": those positive character traits that would have no moral appeal were it not for social conventions established by human artifice. The most important of these virtues is justice, and in the first section Hume offers his so-called "circle argument" to show that justice would not be seen as a virtue in a hypothetical world lacking the relevant social conventions. First, Hume contends, character-based motives are morally more fundamental than actions: we approve of an action only insofar as it indicates some virtuous motive in the agent's character, so that what makes an action virtuous in the first place is the virtuous motive it proceeds from. But this motive must be an ordinary motive in human nature, as opposed to the distinctive moral motive of performing the action because it is virtuous (i.e., a "sense of duty"). After all, this moral motive presupposes that the action already counts as virtuous, and it would be circular to derive the action's virtue from a motive which itself presupposes the action's virtue. And so if justice were a natural virtue, there would have to be an ordinary motive in human nature that could make someone obey the rules of justice. But according to Hume, no such motive can be found: unbridled self-interest leads us away from justice, concern for reputation only goes so far, impartial public benevolence cannot explain all cases of justice and is not even a true element of human nature (contra Hutcheson, we love others only in a limited and discriminating way), and private benevolence for our nearest and dearest cannot explain the universal and impartial nature of justice. Thus there is no motive capable of making justice count as a virtue, not until certain social conventions come into place. Hume closes this section by adding that we evaluate motives largely by