John Locke’s Second Treatise of Government (1689) contains a defense of private property that makes use of the idea of labor-mixing. In §27, Locke writes: ‘[…] for this labour being the unquestionable property of the labourer, no man but he can have a right to what that is once joined to, at least where there is enough, and as good, left in common for others.’ The ‘at least’ clause has become known as the ‘Lockean proviso’. It is usually understood as specifying a limit to labor-based acquisition of private property.

Since libertarians care a lot about private property and its justification, the Lockean proviso has been an important tenet in libertarian theories of justice. In fact it has become common to distinguish ‘right-libertarian’ and ‘left-libertarian’ theories of justice according to their stance on the Lockean proviso. Right-libertarians either reject the Lockean proviso or endorse very weak interpretations of it, while left-libertarians endorse some egalitarian interpretation of the Lockean proviso (which allows appropriation until one has one’s equal share of natural resources or as long as the appropriation is compatible with equality of opportunity for welfare).

In between right- and left-libertarianism, there is room for moderate interpretations of the proviso, and in particular for a sufficientarian interpretation, a sufficiency proviso. It is remarkable that this option has rarely been defended. The resulting theory of justice can be called ‘moderate libertarianism.’ In my article in the Routledge Handbook of Libertarianism, I make a case for moderate libertarianism, so understood. I argue that moderate libertarianism has advantages over both left- and right-libertarianism because it better coheres with the most plausible rationale for endorsing a libertarian theory of justice in the first place.

What is this rationale for endorsing a libertarian theory of justice? It starts with the rather trivial fact that persons are purposive beings. They have the capacity to pursue all kinds of projects. Almost all projects require external resources, and they require being able to count on one’s resources. For that reason, persons as project-pursuers need the opportunity to acquire private property in external resources in one way or another. Following Eric Mack, one can take this to establish a ‘natural right to the practice of private property’. Together with the idea of self-ownership, this natural right can be regarded as the core of a libertarian theory of justice. Note that the project pursuit rationale for libertarianism does not rely on the moral force of Lockean labor-mixing. Rather, private property as a practice is justified as being responsive to persons as project pursuers.

The point of my article is not to defend the project pursuit rationale for libertarianism. What I aim to show is that if one embraces a libertarian theory of justice due to the project pursuit rationale, then one should also embrace a sufficientarian proviso. The basic idea is simple: Without sufficient resources, people are unable to live their lives as project pursuers. Because this is so, a libertarian who advances a libertarian theory of justice because s/he cares about people as project pursuers must also care about everyone actually having sufficient resources for living a life as a project-pursuer. This is why some sort of sufficientarian proviso should be incorporated into a libertarian theory of justice.

In my article in the Routledge volume, I spell out why a sufficiency proviso is superior to the Lockean provisos advocated by left-libertarians like Hillel Steiner or Michael Otsuka and to those advocated by right-libertarians like Robert Nozick and Eric Mack. Here, I will limit myself to presenting some more details about the sufficiency proviso as I conceive it.

First of all, my sufficiency proviso does not apply to specific acts of appropriation, but to the practice of private property as a whole. The practice of private property is justified because private property is necessary for living as a project pursuer, but it can only be justified under condition that it actually enables everyone to live as a project pursuer.

Second, the sufficiency proviso does not unconditionally require us to bring everyone above the sufficiency threshold. The proviso only prescribes that the practice of private property should be designed in a way that makes sure that everyone has sufficient resources to live as a project pursuer, if this is possible without undermining the point of having a practice of private property in the first place. This admittedly does leave quite some room for disagreement about when the point of having a practice of private property is undermined, yet I think this is unavoidable.

Third, the sufficiency proviso does not require that everyone must have sufficient resources left for initial appropriation. What counts is not that everyone can initially acquire things, but that everyone can come to own and use sufficient things. It does not matter whether one gets property via free exchange, gift, or initial appropriation.

Fourth, libertarianism as a theory of justice is silent on the institutions that are most appropriate to meet the sufficiency proviso. It seems natural to think that the proviso speaks for some welfare state institutions, maybe in the form of a guaranteed basic income, maybe in some other form. But the sufficiency proviso need not vindicate welfare state institutions. One can also try to argue that an anarchist society would satisfy the sufficiency proviso.

In the end, I hope that my article can show that moderate libertarianism with its sufficiency proviso is an attractive and interesting variant of libertarianism that is worthy to be more fully explored and discussed.

Beginning in October 2017, Fabian Wendt will be a Research Associate at the Smith Institute for Political Economy and Philosophy at Chapman University. His book Compromise, Peace and Public Justification: Political Morality beyond Justice was published last year by Palgrave Macmillan. This year, he won the Sanders Prize in Political Philosophy.