Contemporary left-libertarian scholars such as David Ellerman, Michael Otsuka, Hillel Steiner, Peter Vallentyne and Philippe Van Parijs root an economic egalitarianism in the classical liberal concepts of self-ownership and appropriation. They hold that it is illegitimate for anyone to claim private ownership of natural resources to the detriment of others, a condition John Locke explicated in "Two Treatises of Government". Locke argued that natural resources could be appropriated as long as doing so satisfies the proviso that there remains "enough, and as good, left in common for others." In this view, unappropriated natural resources are either unowned or owned in common and private appropriation is legitimate only if everyone can appropriate an equal amount or the property is taxed to compensate those who are excluded. This position is articulated in contrast to the position of right-libertarians who argue for a characteristically labor-based right to appropriate unequal parts of the external world such as land. Most left-libertarians of this tradition support some form of economic rent redistribution on the grounds that each individual is entitled to an equal share of natural resources and argue for the desirability of state social welfare programs.