In this essay Rawls investigates ‘justice’ as a property of social institutions (practices). What does it mean to describe an institution as just/unjust? He criticizes a utilitarian conception of justice, according to which an institution is just if it maximizes welfare, on the grounds that a social institution might maximize welfare at the expense of the welfare of certain individuals. Such individuals could legitimately claim that the institution is unjust, and appealing to the fact that the institution maximizes overall welfare would not rebut this charge. The criticism of utilitarianism points towards Rawls’s own conception of the justice of institutions: a just institution is one which all reasonable participants would acknowledge as fair, or an institution in which none of the participants could reasonably complain that they were being treated unfairly. So justice is rooted in fairness. But what determines whether an institution is fair and, hence, just? Rawls’s answer: it’s adherence to the two principles of justice–viz., (1) each person participating in the practice has a right to the most extensive liberty compatible with like liberty for all, and (2) inequalities (in the distribution of benefits and burdens, I think) are arbitrary unless said inequalities work to the advantage of everyone (NOT ‘overall’ advantage), and attach to offices/roles open to everyone.
Why should we think these are the defining principles of a just or fair institution? Rawls’s answer: because they are the principles rational individuals could/would agree to in founding a social institution/practice. (Recall “Outline of a Decision Procedure in Ethics”.)
One of the aspects of this essay I found most interesting is Rawls’s emphasis on the importance of just/fair social institutions for social harmony, cohesion, community, etc. Just institutions enable a form of harmonious social life that would otherwise be impossible. (Injustice creates social conflict, and inevitably derives whatever stability it enjoys from coercion and force.) That strikes me as a very deep and important idea.
That being said, most of the essay is pitched at a very abstract level. I have only a superficial sense of what the ‘two principles’ in practice require and forbid (it’s easy to see that they forbid a social institution like slavery, but what about a social institution like ‘professional baseball’?).