Rawls's idea of the social contract suggests that an act is just if everyone involved in it would agree beforehand that these are the actions that they would reasonably consider taking. As he writes in "Justice and Fairness,"
"A practice is just if it is in accordance with the principles all who participate in it might reasonably be expected to propose or to acknowledge before one another when they are similarly circumstanced and required to make a firm commitment in advance."
Rawls proposes that these conditions are hypothetical, not actual, meaning that they are the conditions that people would impose in a state, called the Original Position, in which they are covered with what he calls the "Veil of Ignorance." The veil means that people do not know at the time that they decide on these conditions whether they are in a state of relative disadvantage or advantage in their society, and they do not know the economic background, race, gender, or other characteristics of their fellow actors. Following Kantian ideas, Rawls assumes that people can use reason working from a universal standard. In these impartial conditions, people are in the best position to decide what is just because they cannot simply decide to advance their own special interests. The lack of self-interest involved in the Original Position is why Rawls refers to his idea as "justice as fairness."
The two positions that Rawls states that people in the Original Position would agree upon are 1) everyone should have as much personal liberty as possible, as everyone is given the same degree of liberty, and 2) social and economic inequality can exist as long as everyone has access to greater economic advantages. In addition, the economic inequalities that exist must still be better than what the person in the lowest position in society would experience under different conditions. Therefore, the two principles cover both civil liberties and economic equality. According to Rawls, the first principle must exist before the second principle, as civil liberties must exist before a society attends to the distribution of economic goods.
Rawls' version of the social contract involved individuals understanding that justice is synonymous with fairness. In this light, individuals enter into a social and political arrangement where they understand that the interests of justice are best served when there is a sense of fairness that underscores the configuration of both realities. Such a design ensures that even those at the bottom rungs of society would be provided with opportunities to improve their own condition. This understanding of the social contract in Rawls' work through the embrace of the veil of ignorance. This mechanism ensures that if individuals had no idea about where they were to fall into a social order, they would make decisions that guaranteed those at the bottom would have some chance at success. Given this, there would be a consideration that while individuals have freedom to do whatever they wish to improve their own lives, the social contract in which Rawls places faith in designing his conception of justice is one where individuals see that those at the bottom of society have some level of legitimate and genuine opportunity for happiness and success.