Veil of Ignorance
Rawls's thought experiment: the principles of justice are those rational agents would choose if they did not know their place in society.
The veil of ignorance is the central device of John Rawls's A Theory of Justice (1971). Rawls asks the reader to imagine rational agents choosing the basic principles of their political society from behind a veil that screens out information about who they will turn out to be — their class, race, gender, talents, conception of the good, or generation.
Behind the veil, no agent can choose principles that favor his own particular position, because he does not know what that position will be. Rawls argues that rational agents in this original position would converge on two principles: equal basic liberties for all, and inequalities permitted only when they benefit the least well-off. The device gives a rigorous structure to the intuition that fairness is impartiality — though critics from Nozick to Sandel have argued that it imports substantive assumptions Rawls denied or smuggles a controversial conception of the person into the framework.