Veil of ignorance
The veil of ignorance, along with the original position, is a method of determining the morality of a certain issue (e.g., slavery) based upon the following thought experiment: parties to the original position know nothing about their particular abilities, tastes, and position within the social order of society.
When the parties are selecting the principles for distribution of rights, positions, and resources in the society they will live in, the veil of ignorance prevents them from knowing about who they will be 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.
As John 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.—John Rawls, A Theory of Justice 
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 veil of ignorance is part of a long tradition of thinking in terms of a social contract. The writings of Immanuel Kant, Thomas Hobbes, John Locke, Jean Jacques Rousseau, and Thomas Jefferson offer examples of this tradition.
"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."
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 the practice does not seem to be justifiable. Perhaps the entire practice would have been abolished without the need for a war to settle things. 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.
David Barr Kirtley
Originally appearing in All The Rage This Year: The Phobos Science Fiction Anthology 3, this short science-fiction story relies heavily on the use of the veil of ignorance to convey its point.
Something strange is happening to me.
We're at Conrad's vacation house, a sprawling mansion that orbits the gas giant Hades-3. (His father owns both the house and the planet.) Conrad is in the living room watching sports. His girlfriend Alyssa is standing by the mirror in the bathroom, fixing her hair. Her friend Kat is sitting near the bay windows, watching the stars and the roiling vermeil clouds on the world below. Dillon is in the kitchen, mixing drinks. Brad is slouched on the sofa, watching everyone with a lazy smile. And I don't know which of them I am. Perception shifts. A few moments of Alyssa, running my fingers through silky hair. A moment of Dillon, using my knife to slice limes for the drinks. A moment of Kat, feeling awe of those looming bands of color, of those constantly churning swirls that look so majestic, and make me feel so insignificant. Then Conrad -- pride at my team's success, at my father's wealth.Then Brad. I feel quite smug. "It's starting to work," I tell them. "You can all feel it, can't you?"
The characters in the story are all under the effects of a drug given to them by Brad that causes each of them to experience each other's thoughts. This causes each character to feel a simulated version of the veil of ignorance which causes them to act much differently than they normally would. The story concludes by having the characters purchase enough drugs to last them a very long time as they are unable to go back to life without the veil of ignorance.
The concept of the veil of ignorance has been in use by other names for centuries by philosophers such as John Stuart Mill, John Rawls, and Immanuel Kant whose work discussed the concept of the social contract. John Harsanyi helped to formalize the concept in economics. The modern usage was developed by John Rawls in A Theory of Justice.
- Rawls, John (1999). A Theory of Justice. Harvard University Press. p. 118. ISBN 0-674-00078-1.
- "Ernie the Attorney : Searching for Truth & Justice (in an unjust world)".
- http://andreaskluth.org/2009/10/28/the-veil-of-ignorance-another-great-thought-experiment/. Missing or empty
- Kirtley, David. "Veil of Ignorance". Retrieved 2014-08-15.
- Harsanyi, J. C. (1953). "Cardinal Utility in Welfare Economics and in the Theory of Risk-taking". J. Polit. Economy 61 (5): 434–435. JSTOR 1827289.
- Harsanyi, J. C. (1955). "Cardinal Welfare, Individualistic Ethics, and Interpersonal Comparisons of Utility". J. Polit. Economy 63 (4): 309–321. JSTOR 1827128.
- Rawls, John (1971). A Theory of Justice. Cambridge, Massachusetts: Belknap Press. ISBN 0-674-00078-1.
- Rawls, John (2001). Justice as Fairness: A Restatement. Cambridge, Massachusetts: Belknap Press.