The choice of the parties in the original position is determined by their interests, their knowledge, and the available options. The knowledge of the parties is restricted to general facts (TJ §24; PL 22–28, 70; JF §§6, 11, 25–26, 35).

The original position models the reasonable constraints on the choice of principles of justice. Placed behind a veil of ignorance, the parties in the original position do not know particular facts about their gender, race, skills, what wealth they own, or similar facts about themselves or those they represent. The parties are also ignorant about particular facts about their society, such as the distribution of religious beliefs, what sorts of natural resources the society has access to, or the distribution ofwealth and opportunities amongst different classes of citizens. The idea is to shield the parties from knowledge that could lead them to propose unfair terms of social cooperation, but let them know enough to choose principles of justice that can deine the basic structure of a well-ordered society. So, the parties know that they have a conception of the good, but not what it is, and they know certain general facts: that they are in circumstances of justice, facts about human nature, psychology, and needs, the general laws of social theory and economics, and that the members of their society afirm a diversity of philosophical, religious, political, and social doctrines (TJ §24).