 The parties are not however completely ignorant of facts. They know all kinds of general facts about persons and societies, including knowledge of relatively uncontroversial scientific laws and generalizations accepted within the natural and social sciences – economics, psychology, political science, biology and other natural sciences (including applications of Darwinian evolutionary theory that are generally accepted by scientists, however controversial they may be among religious fundamentalists). They know then about the general tendencies of human behavior and psychological development, about neuropsychology and biological evolution, and about how economic markets work, including neo-classical price theory of supply and demand. As discussed below, they also know about the circumstances of justice—moderate scarcity and limited altruism—as well as the desirability of the “primary social goods” that are needed by anyone to live a good life and to develop their “moral powers” and other capacities. What the parties lack however is knowledge of any particular facts about their own and other persons’ lives, as well as knowledge of any historical facts about their society and its population, its level of wealth and resources, religious institutions, etc.. Rawls thinks that since the parties are required to come to an agreement on objective principles that supply universal standards of justice applying across all societies, knowledge of particular and historical facts about any person or society is morally irrelevant and potentially prejudicial to their decision.