According to the negative principle of appropriation a person can acquire an unowned resource if doing so respects a certain condition (the Lockean proviso). Contrary to some views, a proviso of this sort is not incompatible with libertarianism. Moreover, no unilateral powers of acquisition can fail to consider the impact on the interests of others. Hence, a doctrine of appropriation must incorporate such a proviso. However, the several interpretations such a proviso can take on various dimensions will be either implausible (...) as a way of taking into consideration the interests of others, or unable to generate the kind and extent of property rights libertarians typically endorse. (shrink)