The theory of A Theory of Justice is that the way to answer questions about justice is to ask what the parties in the original position would choose.
Specifically, Rawls argues that his two principles of justice would be chosen by the parties over utilitarianism.
The features of the original position are listed in the handout. These are the most crucial points.
The parties only care about the people they represent.1
The parties are behind the veil of ignorance. They do not know anything that would enable them to estimate the probability of being helped or hurt by any decision they have to make.
The only thing the parties know about what makes life good for the people they represent is that they need primary social goods. Primary social goods are things that are necessary for any rational plan of life. Rawls thinks that liberty, opportunities, wealth, and a sense of self-worth are all primary social goods (§11, §15).
The parties know the people they represent have psychological limits. They have a sense of justice, meaning they are capable of complying with social rules, but they are also subject to the strains of commitment, meaning that they will not comply with rules that prevent them from satisfying their most important interests.
The parties know that the people they represent are in the circumstances of justice. This is something that Rawls gets from Hume. The idea is that they face moderate material scarcity. They do not live in the Garden of Eden, where rules are unnecessary. Nor do they live in conditions of extreme scarcity, where there is not enough to go around no matter what social rules are adopted. Rather, they live in a world where everyone can benefit from the adoption of social rules, much as Hume imagined everyone would benefit from adopting conventional rules for property rights.2
The very most important feature of the original position is the veil of ignorance. The decision is supposed to be fair because the parties do not know who they represent. In fact, they know almost nothing about their society.
I illustrated this by saying they could not know the probability of being right handed. If they knew that there was a ninety percent chance of being right handed, they would gang up on the lefties. That is not because they have any animus towards the left handers. It is just that this is what the rules tell them to do. The rules say they care exclusively about the people they represent. So if there is a gamble that makes sense with nine to one odds, they would take it. Of course, rules that favored right handers over left handers would be unfair. So Rawls prevents the parties from making rules like that by depriving them of any knowledge of how likely it is that they would represent right handers.
Rawls, John. 1999. A Theory of Justice. Revised edition. Cambridge: Harvard University Press.
Strictly speaking, they care about the next two generations as well, but that is a detail we can ignore for now.↩
The difference between Rawls and Hume is that Rawls worries that rules adopted through conventions may not be as fair as alternative rules decided on by parties in the original position.↩
There was a handout for this class: 24.RawlsOriginalPosition.handout.pdf