The "veil of ignorance" is a method of determining the morality of issues. It asks a decision-maker to make a choice about a social or moral issue and assumes that they have enough information to know the consequences of their possible decisions for everyone but would not know, or would not take into account, which person they are. The theory contends that not knowing one's ultimate position in society would lead to the creation of a just system, as the decision-maker would not want to make decisions which benefit a certain group at the expense of another, because the decision-maker could theoretically end up in either group. The idea has been present in moral philosophy at least since the eighteenth century. The veil of ignorance is part of a long tradition of thinking in terms of a social contract that includes the writings of Immanuel Kant, Thomas Hobbes, John Locke, Jean Jacques Rousseau, and Thomas Jefferson. Prominent modern names attached to it are John Harsanyi and John Rawls.
Spencer J. Maxcy outlines the concept as follows:
Imagine that you have set for yourself the task of developing a totally new social contract for today's society. How could you do so fairly? Although you could never actually eliminate all of your personal biases and prejudices, you would need to take steps at least to minimize them. Rawls suggests that you imagine yourself in an original position behind a veil of ignorance. Behind this veil, you know nothing of yourself and your natural abilities, or your position in society. You know nothing of your sex, race, nationality, or individual tastes. Behind such a veil of ignorance all individuals are simply specified as rational, free, and morally equal beings. You do know that in the "real world", however, there will be a wide variety in the natural distribution of natural assets and abilities, and that there will be differences of sex, race, and culture that will distinguish groups of people from each other.
It has been argued that such a concept can have grand effects if it were to be practiced both in the present and in the past. Referring again to the example of slavery, if the slave-owners were forced through the veil of ignorance to imagine that they themselves may be slaves, then suddenly slavery may no longer seem justifiable. A grander example would be if each individual in society were to base their practices off the fact that they could be the least advantaged member of society. In this scenario, freedom and equality could possibly coexist in a way that has been the ideal of many philosophers. For example, in the imaginary society, one might or might not be intelligent, rich, or born into a preferred class. Since one may occupy any position in the society once the veil is lifted, the device forces the parties to consider society from the perspective of all members, including the worst-off and best-off members.
The version proposed in 1971 by American philosopher John Rawls in his "original position" political philosophy is based upon the following thought experiment: people making political decisions imagine that they know nothing about the particular talents, abilities, tastes, social class, and positions they will have within a social order. When such parties are selecting the principles for distribution of rights, positions, and resources in the society in which they will live, this "veil of ignorance" prevents them from knowing who will receive a given distribution of rights, positions, and resources in that society. For example, for a proposed society in which 50% of the population is kept in slavery, it follows that on entering the new society there is a 50% likelihood that the participant would be a slave. The idea is that parties subject to the veil of ignorance will make choices based upon moral considerations, since they will not be able to act on their class interest.
As Rawls put it, "no one knows his place in society, his class position or social status; nor does he know his fortune in the distribution of natural assets and abilities, his intelligence and strength, and the like". The idea of the thought experiment is to render obsolete those personal considerations that are morally irrelevant to the justice or injustice of principles meant to allocate the benefits of social cooperation.
The concept of the veil of ignorance has been in use by other names for centuries by philosophers such as John Stuart Mill and Immanuel Kant whose work discussed the concept of the social contract, Adam Smith with his "impartial spectator", or the ideal observer theory. John Harsanyi helped to formalize the concept in economics, and argued that it provides an argument in favor of utilitarianism rather than an argument for a social contract. The usage of the term by John Rawls was developed in his 1971 book A Theory of Justice. Modern work tends to focus on the different decision theories that might describe the choice of the decision-maker "behind the veil".