Suppose we assume that the parties in the original position took Kahneman and Tversky's prospect theory as constituting their general knowledge of human psychology that survives through the veil of ignorance. How would this change the choice situation of the original position? In this paper, I present what I call ‘prospect utilitarianism’. Prospect utilitarianism combines the utilitarian social welfare function with individual utility functions characterized by Kahneman and Tversky's prospect theory. I will argue that, once prospect utilitarianism is on the (...) table, Rawls's original arguments in support of justice as fairness as well as his arguments against utilitarianism are, at best, inconclusive. This shows that how implausible a choice for utilitarianism in the original position is heavily depends on what one assumes to be general knowledge of human psychology that the original contracting parties know. (shrink)