This proviso looks both backwards and forwards. My rights rest on a history of just acquisition and just transfer. But my acquisition must also satisfy Locke's proviso, and that depends on its future impact. To evaluate claims about rights, Nozick's affluent readers had to study both the history of their society and its future. This is why Nozick offers the perfect lens through which we can examine relations between affluent philosophy and the broken world.

The official role of Locke's proviso is to determine who owns what. But haven't we just seen not only that affluent holdings rested on a history of flagrant injustice, but also that Nozick's principle of self-ownership is internally incoherent? Don't we already know that no affluent person owned anything? If so, why bother with Locke's proviso?

As philosophers, reality is not our main concern. Nozick never claimed to defend existing property rights, and he cannot be blamed for those inattentive affluent readers who thought that he had. We can explore his ideal theory of justice even if it does not match reality. Locke's proviso plays a crucial role in that ideal, and may render it more appealing.