Hume's natural history of chastity begins with a number of prima facie plausible assumptions. Men face an assurance problem, when it comes to raising children. Hume's natural history of chastity points to an alternative account of how one's ancestors manages to establish conventions for delayed social exchanges. Hume recognizes that social exchange conventions could never establish the large-scale societies if one's tendency to discount the future was left unchecked. In order to complete his natural history of justice, he explains how one's ancestors manages to overcome this obstacle. Hume rejects any naive solution which suggests that agents conquer their impulsivity through strenuous effort and a repeated resolution to be strong-willed sensible knaves acknowledge that society could not exist without rules of justice, but they think it is best to opportunistically violate them. Knaves are those who lack feelings of repugnance towards cheating. But these emotions requires human beings to achieve self-control.