David Hume argues that reflections upon public utility explain the psychological foundations of justice and the moral feelings attendant on it. Adam Smith objects that Hume’s theory of justice is psychologically implausible. A just punishment attracts the approval of every citizen on Hume’s alleged view. Not every citizen can consider the abstract public interest every time, Smith observes, so Hume can’t have explained all of justice. I argue, in response, that Smith’s objection has not accounted for all of the causal processes that Hume draws upon in support of reflections upon public utility. Conventions establish the very possibility of public interest, and socializing processes lend the public interest its moral salience. Human nature includes a species-general passion for acquiring property for the sake of family. The motivational centrality and universal scope of this passion, coupled with the dramatic psychological power of sympathy, generates the first moral feelings. Social conditioning develops those feelings into attitudes about reward and punishment. Hume’s theory of justice, with his conjectures about sociocultural processes, is both psychologically plausible and more complex than commentators tend to appreciate.