 The nature of justice in acquisition is a source of controversy amongst libertarians. Assuming that the external resources we have in mind are initially unowned, one might argue that specific individuals can appropriate resources as private property by “mixing” their self-owned powers with the resources concerned. This thought, which we find in the work of John Locke (Locke 1689: Book 2, chapter 5), is that individuals integrate something they already own (their labor) with something initially unowned (say, a piece of land), and, thereby, come to own what they initially did not own. However, some libertarians, such as Nozick, follow Locke in arguing that appropriation through the exercise of self-owned powers is just only if it does not harm those who, following appropriation, lose access to the resource. This condition (often referred to as the Lockean Proviso) can be elaborated in various ways. In Nozick’s influential statement of the libertarian view, the condition is apparently elaborated as follows (see Nozick 1974: 174–182; and, for helpful interpretation, Wolff 1991: 107–115): an act of appropriation of a previously unowned resource is just only if no person is thereby made worse off than they would be in a world where all external resources remain unowned. In a world in which all external resources remain unowned, each person would be able to reach a certain level of welfare by using the resources that lie about unowned. For any given individual, i, let us denote this welfare level as Wi. A given act of appropriation is just, then, provided that, post-appropriation, each individual remains able to reach at least Wi. (Note that Wi may differ between particular individuals because of their unequal abilities to produce things in the “state of nature” in which all external resources remain unowned.)