 Philosophers writing on justice have observed that it has two different faces, one conservative of existing norms and practices, the other demanding reform of these norms and practices (see Sidgwick 1874/1907, Raphael 2001). Thus on the one hand it is a matter of justice to respect people’s rights under existing law or moral rules, or more generally to fulfil the legitimate expectations they have acquired as a result of past practice, social conventions, and so forth; on the other hand, justice often gives us reason to change laws, practices and conventions quite radically, thereby creating new entitlements and expectations. This exposes an ambiguity in what it means to ‘render each his due’. What is ‘due’ might be what a person can reasonably expect to have given existing law, policy, or social practice, or it might be what the person should get under a regime of ideal justice: this could mean what the person deserves, or needs, or is entitled to on grounds of equality, depending on which ideal principle is being invoked.