6 ideas
To derive fair principles for society, imagine rational parties choosing the rules under conditions where no one knows their place in advance. The fairness of the agreement comes from the symmetry of everyone's situation at the moment of choice, which prevents bargaining advantages from distorting the outcome.
Parties choosing principles of justice are deprived of knowledge of their own race, class, talents, gender, and conception of the good. Because no one can tailor the rules to favor their actual circumstances, they are forced to choose principles acceptable from every possible position.
Facing total uncertainty about which position they will occupy, rational choosers maximize the minimum outcome rather than gamble on average utility. This makes them protect the worst-off position, since they might end up there and cannot accept principles that sacrifice some lives for aggregate gains.
Social and economic inequalities are justified only if they work to the greatest benefit of the least advantaged members of society. Unequal distributions are permissible not because they are deserved, but because they raise the floor for those at the bottom.
The distribution of native abilities and the family one is born into result from a lottery no one earns or deserves. Therefore the rewards flowing from those talents cannot be claimed as pure desert, and society may treat the distribution of natural assets as a common resource.
Justify moral principles by moving back and forth between abstract principles and concrete considered judgments, revising each until they cohere. Neither intuitions nor theory has final authority; the goal is mutual adjustment until the two align into a stable balance.