Robert Nozick’s Anarchy, State, and Utopia is widely acknowledged as a brilliant work of political philosophy, even by many theorists who reject its key conclusions. Among his enduring contributions are the arguments he formulates for the stringency of property rights, highlighting their essential connection to the exercise of personal autonomy. For example, while not (as often claimed) adopting self-ownership as the mainspring of his defense of libertarian rights, he famously wrote that: “Seizing the results of someone’s labor is equivalent to seizing hours from him and directing him to carry on various activities…The process whereby they take this decision from you makes them a part-owner of you; it gives them a property right in you” (emphasis in original). ASU, 172.
In this process, he addresses many of the considerations that have been invoked by others to limit the scope of ownership rights. This “parade of horribles” includes a stranded hiker whose survival depends on breaking into a deserted cabin (“Cabin”) and a misanthropic inventor who is unwilling to lend humanity his asteroid-destroying device (“Asteroid”). See my Nozick’s Libertarian Project: An Elaboration and Defense, 130.
Nozick’s ingenious solution to such hypotheticals is his adaptation of the “Lockean proviso,” which conditions his allegiance to the institution of private property on it not worsening the welfare of non-owners. Generally, he argues that the economic vitality of free markets will satisfy this proviso, thereby eliminating the need to defend private property on a utilitarian basis. See ASU, 177. However, it also turns out that what he calls the “historical shadow” that follows the disposition of property can also solve puzzles like Cabin and Asteroid. A near final draft of my analysis of this idea in Nozick’s Libertarian Project (130-33) is reproduced below (the relevance of Nozick’s historical shadow to poverty-relief is discussed in a subsequent section of my book).
* * *
In our discussion of Locke’s theory of original acquisition in Chapter 2, we saw that Nozick interprets Locke’s famous proviso as conditioning just initial appropriation on the claimant improving the property in some significant fashion and not worsening the position of others. The later qualification would preclude an agent from appropriating all the water in the desert or the like. We noted the existence of certain complications relating to the selection of the appropriate baseline to be used to test the “no worse off” condition, which he himself calls attention to by asking at one point, “Lockean appropriation makes people no worse off than they would be how?” (ASU, 177). Although Nozick is less than clear on this point, he appears to think that the proviso’s anti-monopoly prohibition rests on the circumstance that in such cases the owner’s full capitalist property rights are making people worse off than they would be under other forms of ownership that might have evolved from a state of nature. (see ASU, 177).
The Lockean proviso also has implications for Nozick’s principle of “justice in transfer.” For example, not only would it be unjust to initially appropriate all the water in the desert, it would also be morally illegitimate to first appropriate some of it and then, through a series of subsequent purchases, to acquire the rest (see ASU, 179). Therefore, the Lockean proviso casts what Nozick calls a “historical shadow” on property, such that it,
excludes [the owner from] transferring it into an agglomeration that does violate the Lockean proviso and excludes his using it in a way, in coordination with others or independently of them, so as to violate the proviso by making the situation of others worse than their baseline situation. (ASU, 180).
Nozick holds that the proviso would apply even if the monopolist corners the market in a critical resource as a consequence of circumstances outside of his or her control. Accordingly, if as a result of natural causes all the water holes in the desert dry up but one, the owner of the remaining one may not charge what he likes, because:
This unfortunate circumstance, admittedly no fault of [the owner], brings into operation the Lockean proviso and limits his property rights (footnote omitted). Similarly, an owner’s property right in the only island in an area does not allow him to order a castaway from a shipwreck off the island as a trespasser, for this would violate the Lockean proviso. (ASU, 180).
In light of this comment, Nozick may have anticipated the sort of counter-examples to libertarian property rights conceived by his critics and sampled above. It is tempting to conclude that just as the owner of the island may not order the castaway back into the sea, the owner in Cabin may not prevent hiker from using it to survive. By the same logic, the owner of the asteroid-destroying devise cannot deprive humanity of its use.
However, upon further reflection, the Lockean proviso (as construed to this point) is not clearly applicable in Cabin and Asteroid. As you may recall from Chapter 2, Nozick argues that Lockean appropriation does not leave subsequent generations worse off because capitalism’s economic vitality, relative to any non-capitalist alternative, provides at least an equal range of economic opportunity for those who did not acquire natural resources in the initial round. We must therefore assume that this is exactly what has happened in these two scenarios.
Accordingly, in Cabin, but for the virtues of private property the cabin might not exist, and hiker is not necessarily made worse off (relative to a non-capitalist baseline) by being denied access. Furthermore, in Asteroid we may suppose that Lockean appropriation created the economic conditions that made the development of the equipment possible, and so society is not necessarily made worse off (relative to a non-capitalist baseline) by being denied its use. Thus, neither hiker nor the general public respectively would, under the proviso, have an unambiguous right to the Cabin or the equipment.
I believe there is a plausible response to this challenge. The answer relies on the fact that as discussed early in Chapter 2, the proviso has its origin in Locke’s insistence that original appropriation not violate any other party’s natural right to self-preservation. It is this concern that causes him to impose the condition that any reduction to private property leave “enough and as good” for others.
This principle of “equal right” is an inescapable aspect of our ordinary moral consciousness and is acknowledged by Nozick in his argument for side constraints (see Chapter 1). Therefore, the appropriate question in Cabin and Asteroid is not whether those in danger would fare better relative to a non-capitalist baseline, but whether their equal right of self-preservation is being violated. Clearly, the owners are abusing their property rights in Cabin and Asteroid, and thus come within reach of the proviso, properly understood.
I contend that the same analysis should apply to the “all the water in the desert” and the castaway cases. When the original owners of these natural assets privatized them, they did so subject to the condition that they respect the equal rights of others to self-preservation. At the time of first acquisition, this obligation was satisfied by the availability of other unclaimed land or water holes. However, since each subsequent transferee of these resources inherits the advantages of individual ownership, it is only fair, as Nozick recognizes, that: “Each owner’s title to his holding includes the historical shadow of the Lockean proviso on appropriation.” (ASU, 180). Accordingly, there is no need to resort to hypothetical welfare baselines to resolve cases of this type; the continuing obligations of those who acquired property from the original appropriator will do the trick.
On the other hand if, contrary to fact, collective forms of property ownership actually outperform “pure” capitalism in terms of the standard of living enjoyed by most people, then privatization would clearly worsen the position of others and be morally bankrupt. Therefore, Nozick’s principle of justice in acquisition must as a general matter rely on the assumption of capitalism’s economic superiority. Thus, the “all the water in the desert” and Cabin scenarios should be seen as special cases where the economic advantages of capitalism are insufficient by themselves to satisfy the “no worse off” requirement.
Finally, note that at least with respect to his justification of private property, Locke recognized only an equal right of self-preservation and not a general right to welfare. Accordingly, in construing cases like Cabin, the owner’s full property rights would be limited only where the threatened loss of life or serious injury was clear, immediate and avoidable only through the use (or if absolutely necessary, the destruction) of private property. It would also require that the beneficiaries of any emergency appropriation of private property fully compensate the owner for its use or destruction.
 After noting that he is uncertain as to how we should select the relevant baseline, Nozick refers to “differing theories of appropriation.” (ASU, 177). This suggests that the baseline would be selected from a range of other (non-capitalist) ownership arrangements. On the other hand, in his discussion and tentative endorsement of Fourier’s proposal for a guaranteed minimum, he appears to understand this guaranty as representing compensation for the foregone opportunity to engage in communal activities only possible in the pre-property world. As explained in the text, this understanding of our obligations to the disadvantaged does not require the selection of any specific capitalist baseline. (ASU, 178-79n)
 Richard Arneson was kind enough to point this out to me in a private communication.