After the parties in the original position agree on principles for the basic structure of society, they set themselves the task of identifying principles for individuals (TJ 93–101). Among such principles, some are permissions, whereas others are requirements (TJ 94). Permissions indicate which acts we are at liberty to do or not do, and further subdivide into indifferent acts, whose performance (or lack thereof ) is insignificant from a moral point of view; and supererogatory acts, which are not morally mandated but whose performance is nevertheless commendable. Requirements are mandatory, and can be either obligations or duties.

Following Brandt (1964) and Hart (1958), Rawls conceives of an obligation as a requirement to take, or refrain from taking, some course of action, which differs from a duty on a number of grounds (TJ 97). First, obligations are either voluntarily undertaken or incurred in some way that tracks our agency, such as by making a promise, signing a contract, or damaging someone else’s property whilst using it. Second, the content of obligations is defined by the rules of an institution or practice which set requirements that their participants or members must comply with. Therefore, obligations derive from playing specific roles within social practices or institutions and fall on us upon joining these practices or institutions either explicitly or implicitly (such as by signing a contract, running for public office, or driving a car). Finally, obligations are owed to specific individuals in virtue of our interaction or cooperation with them within those institutions and practices. Duties, on the other hand, fall on us independently of what we commit to do, which role we cover, or which action we have previously undertaken; their content is not identified by institutions or practices; and they often have either unspecified or universal addressees.