the rules of justice would be pointless. Real-world cases also illustrate the idea: close personal relationships bring one's private belongings into common ownership, and free goods like air and water are allowed unrestricted use. And this general point, Hume says, reinforces three earlier points: (1) Public benevolence cannot be why we obey the rules of justice, for it would only make these rules pointless. (2) Moral rationalism cannot make sense of justice: mere abstract reasoning can neither account for the fact that justice hinges on specific background conditions, nor produce the concern for our interests that originally leads us to establish the rules of justice. (3) Justice is an artificial virtue: though the whole purpose of justice is to serve our interests, the connection between justice and our interests dissolves in the absence of the relevant social convention. For without this convention, wholehearted pursuit of the public interest would make justice pointless and unrestrained pursuit of private interests would leave justice in ruins. And likewise, without this convention, certain individual acts of justice (e.g., returning money to a villain) would run contrary to our private interests and even the public interest: such unfortunate acts are worth performing only because of our convention-based expectation that others will follow our example and reinforce the "whole system", which does serve everyone's advantage. Hume's answer to the second question is that our approval of justice and disapproval of injustice is based in sympathy with the public interest. Justice was established to serve our interests, but when society grows large enough, we might lose sight of how injustice threatens social order. Fortunately, the threat can be made vivid again when I myself am the victim of injustice, or when I impartially sympathise with others threatened by injustice. Their sympathetically communicated negative feelings form the basis of my disapproval of injustice, and this evaluation subsequently extends to my own behavior through the influence of general rules and sympathy with the opinions of others. Three additional factors then reinforce these moral sentiments: (1) Public leaders propagandise on behalf of justice (contra Mandeville, this technique works only by appealing to and intensifying moral sentiments we already have). (2) Parents instill children with a reliable and deeply rooted concern for the rules of justice. (3) Concern for reputation makes us scrupulously avoid injustice as a matter of personal principle. Sections 3–6 The next four sections see Hume completing his