Friedman critiques Matt Zwolinski’s essay on the complicated nature of private property.

David D. Friedman, son of Nobel laureate Milton Friedman, is a leading proponent of anarcho-capitalism, the theory that the state is an unnecessary evil and that all services, including the law itself, can be provided by voluntary cooperation in the private economy.
While Friedman holds a Ph.D. in physics from the University of Chicago, he is chiefly known for his scholarly contributions to economics and law. He is the author of five books of non-fiction as well as the novels Harald and Salamander. In The Machinery of Freedom: Guide to a Radical Capitalism, Friedman argued that an economic analysis of impact of state action points to an anarchist conclusion. In Law's Order: What Economics Has to Do with Law and Why It Matters, he shows how directing the law to seek economic efficiency can lead to the achievement of justice.
Friedman stands in contrast to many other anarchists because of his "consequentialist" approach. Rather than argue that humans have inviolable natural rights which it is always wrong to violate, he uses cost-benefit analysis to assert that a world without government is measurably better than one ruled by states.

Matt Zwolinski, in his most recent essay, merges two different philosophical issues in a way that obscures the difference between them. One, the problem of initial appropriation of land, is a hard problem, at least for libertarians: How do people get ownership rights over uncreated property, such as the surface of the earth, sufficient to give them a right to prevent others from using it. One is, at least for libertarians, an easy problem: How do individuals get ownership over created property, such as a railroad train, sufficient to prevent others from using it. Merging the two is a particularly unfortunate philosophical move since the easy problem provides a possible solution to the hard one.

To see why the second is an easy problem, try applying Zwolinski’s argument to what libertarians view as the most fundamental property claim, my ownership of my own body. You have a rifle and enjoy shooting things. I am standing between you and one of the things you would like to shoot. That’s no problem—you have a very powerful rifle, capable of putting a bullet through my body en route to your target. Is Zwolinski prepared to argue that if I forcibly prevent you from doing so, you “lack precisely the kind of negative freedom that libertarians purport to be concerned with—freedom from liability to physical interference by other human beings?” If he is not, why is he willing to make that argument when what I forcibly prevent you from using or damaging is not my body but my created property, objects which exist only due to the application of human effort to the (at this point in my argument) commonly available uncreated property? He puts his argument in terms of the efforts of “men with guns,” policemen, but nothing in it depends on whether other people forcibly defend my rights or I do it for myself.

Part of his response is that “But lack of money would be no obstacle to a solitary man on a desert island. And this is because money is an essentially social device. It derives its value from a system of norms that are socially recognized and socially enforced.” But the existence of money is in no way central to the existence of property rights. What is being enforced when a woman who cannot afford a ticket is ejected from a train is not a social convention about money but the right of the owner of the train to control who uses it. A solitary man on a desert island, like the woman ejected from the train, is constrained by the absence of objects he has a right to use; in the former case things he would like to use are physically absent, in the latter they are physically present but belong to someone else.

I started this comment by suggesting that rights to created property provided a possible solution to the problem of rights to uncreated property. The argument, from an old piece of mine, goes as follows:

You wish to stand on a certain piece of common property. I am there already. You have the same right as I do to stand there, but you do not have a right to move or injure me, hence you cannot exercise your right to stand there without acting unjustly. I have not appropriated the land I am standing on in the usual sense of the term, but I have “de facto” appropriated it for as long as I stand there, not by altering the nature of your right to the land but by making it impractical for you to exercise it without violating other rights.

You have (somehow) acquired a rifle and ammunition, and wish to engage in target practice. The whole world is your target range. But you cannot fire in my direction-​-​because you do not have the right to injure me. My existence and my present location decrease the value of your rights to you without violating or reducing those rights. You still have a right to shoot anywhere you like. You do not have a right to shoot me. If in some ingenious way you can exercise the former right without violating the latter prohibition (for example, by using a weapon shooting harmless water drops or a radar controlled gun which will not go off when it is pointing exactly at me) you may do so. …

… I plant wheat in a field. You come and want to plant wheat in the same field. I point out to you that the field is common property which you are welcome to use, but the wheat I have planted is my property (the result of my labor in gathering seeds, watering them so they would sprout, etc.) and you do not have the right to disturb it. Any way you can figure out to exercise your right to the field without violating my right to the wheat is fine with me.

This example can, perhaps, be expanded into a full justification for “property rights” in uncreated property. Seen from this viewpoint the original right of freedom of action need never have been infringed. When I “mix” my labor with the land I make it inconvenient for you to use the land without violating my right to my labor. If you figure out a way of doing so, fine. You still have the right of freedom of action, and that right is still limited, as it always was, by my right not to have my private property violated.