(A) Possession of External Things

Aquinas considers whether it is natural for human beings to possess external things. He concludes that it is, saying, ‘God has supreme dominion over all things; and, according to His providence, He has ordained certain things for the support of man’s body. For this reason man has a natural dominion over things with regard to the power to make use of them’. ^{Footnote 12} The purpose of certain material resources is to sustain human beings on earth, and to that end it is natural for human beings to use and manage such resources.

Aquinas goes on in articulus 2 to consider the lawfulness of private property. He distinguishes between an individual’s right to use material resources for sustenance, and to hold private property. He argues that while the law of nature prescribes a right for human beings to use material goods for sustenance, private property is an addition to the law of nature that flows from human reason and is restricted by that primary requirement of the law of nature. Aquinas adopts a practical view of the benefits of private property in his responsio, saying:

As John Finnis notes, all of these justifications are based on the contribution private property can make to the common good, as opposed to any metaphysical connection between the possessor and the property. ^{Footnote 14} The instrumental arguments advanced are familiar ones: material resources are put to more productive use where they are privately owned, society is more clearly ordered and regulated under such a system, and disputes amongst men are minimised. ^{Footnote 15} Private property is conceived of as a useful tool for efficient and effective social co-ordination. ^{Footnote 16} However, it is for Aquinas always subject to the law of nature’s requirement that all men have the right to access and use material resources for their sustenance. ^{Footnote 17}

Aquinas’ theory of law provides an important, and in some respects contentious, backdrop to his approach to property. ^{Footnote 18} A detailed exploration of this debate, and of Aquinas’ typology of law, is beyond the scope of this article. However, the position of private property within this typology is made clear when Aquinas states:

Thus, Aquinas argues that natural law does not dictate that all possession should be in common. Aquinas contends that the natural law can be changed by addition, “…for many things advantageous to human life have been added over and above the natural law, both by the Divine law and by human laws.” ^{Footnote 20} Such additions form the secondary principles of the natural law. ^{Footnote 21} Aquinas explains private ownership in these terms, as an addition to the natural law by human law:

For Aquinas, any additions introduced through human law are subject to the law of nature. ^{Footnote 23} A human law may be a general conclusion derived from the principles of the law of nature, or it may be a specific application of those general principles. He argues that these two kinds of derivation are linked to the law of nature to different degrees: “those things which are derived in the first way are not contained in human law simply as belonging to it alone; rather, they have some of their force from the law of nature. But those things which are derived in the second way have their force from human law alone.” ^{Footnote 24}

In developing this distinction between modes of derivation from the law of nature, Aquinas discusses the ius gentium as one of the divisions of human law, and situates private property within that category in his typology of law. He explains:

The above-quoted passage demonstrates a degree of ambiguity in Aquinas’ theory on the appropriate categorisation of the ius gentium. ^{Footnote 26} On the one hand, he says, “positive law is divided into the ius gentium and “civil law””, and on the other hand, he says of the ius gentium, “this kind of law belongs to the law of nature”. Such duality appears to be a distinctive characteristic of Aquinas’ ius gentium—it is a discrete category of law, but it straddles human and natural law. ^{Footnote 27} It is at once enacted and natural, and includes private possession of property. ^{Footnote 28} Private ownership is a rational derivation from the law of nature’s requirement that human beings must have use of the earth’s material resources for their sustenance. Accordingly, it forms part of the ius gentium and lies between the law of nature and positive law.

(B) Superflua and Necessity

Whenever someone enjoys a superabundance of material goods, Aquinas says that someone else is necessarily suffering want, because of the limited nature of the earth’s resources. In light of this, he argues, “whatever anyone has in superabundance is due under the natural law to the poor for their succor”. ^{Footnote 29} For Aquinas, because there are many persons in need who cannot practically be sustained from the same material resources, the individual possessor judges for him or herself how his or her property should be dispensed to those in need. ^{Footnote 30} However, the obligation to distribute superflua is a matter of justice—private ownership loses its lawful character if others who are in need are excluded from using material resources. ^{Footnote 31} Aquinas argues:

(C) The Sin of Theft

Aquinas goes on to consider offences against private property. He notes that theft is a sin, but he considers whether it is lawful to steal in circumstances of necessity, and in doing so, stresses again that human law is subject to the dictates of natural law. ^{Footnote 33} Although as we saw in the last section, the distribution of ‘superflua’ is ordinarily a matter for the individual in possession of property, Aquinas holds that theft does not occur in situations where material resources are used for basic sustenance. Such cases are narrowly defined as follows:

In addition, anyone can take property from another on behalf of a needy individual. ^{Footnote 35} Thus, the presumptive individual discretion to determine the distribution of superflua is trumped by circumstances of urgent need that cannot be otherwise satisfied.

(D) Aquinas on Property—Summary

From this brief overview, it should be clear that Aquinas’ approach is relatively non-prescriptive in relation to private ownership, and understands ownership in non-absolutist terms. ^{Footnote 36} The law of nature demands that human beings must be able to use the earth’s material resources to secure their survival. Private property is a derivation of human reason from this basic precept of natural law, which is regarded by Aquinas as a useful addition to the law of nature, because it contributes to the common good by helping to secure the efficient and peaceful use of the earth’s resources. As such, it is part of the ius gentium, which is the body of law derived by human reason from the precepts of the law of nature and closely rooted in the law of nature. It is subject to the duty in justice to distribute superfluous property to those in need, and to the qualification that those in narrowly defined circumstances of urgent need can take another’s property without committing the sin of theft.

(A) Land-Use Decision-Making, Human Flourishing, and Necessity

In ‘Land Virtues’, Eduardo Peñalver draws on Thomistic property theory in proposing a break from economic analysis in the context of land-use decision-making. ^{Footnote 43} As an alternative, Peñalver argues for “[a] theory of owner obligation rooted in the Aristotelian tradition”, based on virtue ethics. ^{Footnote 44}

Peñalver characterises virtue ethics as an important source of guidance in delineating the respective scope of individual freedom and collective decision-making in relation to land-use. ^{Footnote 45} He defines virtues as “…acquired, stable dispositions to engage in certain characteristic modes of behaviour that are conducive to human flourishing.” ^{Footnote 46} He argues that flourishing is a collective endeavour, involving mutual social obligations. ^{Footnote 47} Reasons for action, as well as external actions, are important, since virtuous activity requires proper motivation rather than mere compliance with rules. ^{Footnote 48} The standard applied is the conduct of the virtuous person, which in turn is based upon “… an objective conception of what it means to live well or flourish in a distinctively human way.” ^{Footnote 49}

For Peñalver, the role of law is to intervene where markets fail and to encourage and facilitate human virtue and flourishing. ^{Footnote 50} For instance, Peñalver argues that the law can enforce specific moral obligations to help those who might be harmed by immoral decisions of owners. ^{Footnote 51} He relies on Aquinas to support the contention that law can be used to require people to act virtuously, and over time may convert them to doing so voluntarily. ^{Footnote 52} Finally, he argues that law can assist in clarifying how those who wish to act virtuously should behave, and in coordinating such actions. ^{Footnote 53} At the same time, Peñalver acknowledges the significance of autonomy to human flourishing, and suggests that determining the appropriate distribution of decision-making power between individuals and the state is ‘a difficult puzzle’, which requires a broader perspective than that afforded by economic analysis. ^{Footnote 54} He welcomes the fact that virtue theory brings to the forefront the tensions that exist between the various values implicated in property and land use law and requires those tensions to be addressed directly. ^{Footnote 55}

Peñalver details how virtues essential to human flourishing can be fostered through land-use decision-making. He begins with industry, relying directly on Aquinas’ practical justification of private ownership to support the contention that private possession encourages the productive use of land. ^{Footnote 56} He argues,

Where that incentive fails, more coercive legal measures can be used to encourage efficient land-use. However, Peñalver again turns to Aquinas to stress that industry is not the exclusive or primary virtue to be considered in land-use decision-making: private possession is permissible to achieve industry, but is subject always to the ultimately common right of men to use the earth’s resources to sustain themselves. ^{Footnote 58} Accordingly, he argues that industry is just one of several ‘land virtues’ that should influence land-use decision-making. Although as was seen above, the justification of private possession of property offered by Aquinas (and relied upon by Peñalver) was not framed directly in terms of virtue, it could be captured in particular circumstances by the Thomistic virtues of prudence (concerned with practical reasonableness) and/or justice (focused on giving to each their due). As Aquinas put it, “… every virtue that causes a good judgment of reason may be called prudence: every virtue that causes actions to fulfill what is right and due may be called justice…” ^{Footnote 59} The decision to adopt a private ownership system could be deemed prudential, while actions taken on foot of that system could be regarded as required by justice, provided that the standards set out by Aquinas for prudence and justice were satisfied.

In relation to justice, Peñalver argues that legally coerced redistribution, either of land or of money, may be required in certain circumstances. He does not specifically reference Aquinas in developing his theory of the virtue of justice. However, his argument aligns closely with Aquinas’ treatment of superflua, for example when he says:

For Peñalver, owners’ obligations are not narrowly determined by the urgent material needs of others, but rather are more broadly determined by the concept of human flourishing. For example, he includes within the requirements of human flourishing, “… the material resources necessary for social participation, moral training, language acquisition, and the nutritional resources necessary for physical and mental development.” ^{Footnote 61} On this point, concerning the extent of an owner’s sharing obligations, Peñalver appears to go further than was contemplated by Aquinas. For example, in his discussion of the virtue of charity, Aquinas stated that giving is usually only required from resources available to an individual after satisfying the needs of himself or herself and those of any dependents, with an owner’s core obligation being to respond to “evident and urgent necessity” on the part of others that cannot be met through other means. ^{Footnote 62}

Peñalver contends that a recipient’s urgent and acute needs, their connections with particular property, their dignity, and/or mutual relationships of reliance between the giver and the recipient could all warrant compelled redistribution of property in-kind. ^{Footnote 63} To illustrate this point, he cites the defence of necessity, which prevents an owner from interfering with the use of private property by another to satisfy dire and immediate needs. ^{Footnote 64} He argues that this shows that the law already recognises and protects need-based claims over privately held property, thereby supporting his thesis. Similarly, writing with Sonia Katyal, he invokes Aquinas’ argument that theft does not occur when property from another’s superflua is used in circumstances of urgent necessity to argue for the normative and legal plausibility of broader consideration of necessity in the context of property offences. ^{Footnote 65} Peñalver and Katyal advocate necessity as a defence for those who use the property of others, without permission or other lawful basis, to meet their economic and/or physical needs, or in the alternative, for consideration of necessity as a mitigating factor in respect of sentencing for property offences committed in such circumstances. ^{Footnote 66} Drawing on Aristotle, Adam Smith, Amartya Sen and Elizabeth Anderson (although not Aquinas), they suggest that the standard against which necessity is assessed should potentially involve access to more than merely subsistence resources, extending instead to all those resources needed to participate minimally in the life of a particular community. They reason that the numbers of individuals who might need to violate property laws to avoid imminent physical harms are likely to be very low, and accordingly argue for a conception of necessity that is dynamic and context-dependent. They contend that while the necessity doctrine might still, against the backdrop of this broader understanding of necessary resources, be qualified in some way, a showing of imminent physical harm might not be required to establish a defence of necessity. ^{Footnote 67}

(B) The ‘Social-Obligation Norm’, Community, and Human Flourishing

Gregory Alexander characterises human flourishing as a basis for imposing duties on owners. ^{Footnote 68} He argues for explicit recognition of a “social obligation norm” that he identifies as implicit in American property law. He bases this norm on an Aristotelian conception of human flourishing, according to which life within a community of social relations is necessary, as well as “…the capacity to make meaningful choices among alternative life horizons, to discern the salient differences among them, and to deliberate deeply about what is valuable within those available alternatives.” ^{Footnote 69} He stresses that resources, as well as virtues, are necessary for individuals to flourish. ^{Footnote 70} Accordingly, he argues that distributive justice is required, which generates obligations for owners to give others the resources needed for human flourishing on a non-reciprocal basis. ^{Footnote 71} Specifically, Alexander contends, “…an owner is morally obligated to provide to the society of which the individual is a member those benefits that the society reasonably regards as necessary for human flourishing.” ^{Footnote 72} This obligation is limited by the autonomy interests of the owner, which will prevail if they are weightier than the interests implicated by the social obligation norm. ^{Footnote 73} Alexander concludes that owners’ interests can justifiably be curtailed “…on the basis of cultivating the conditions necessary for members of our communities to live well-lived lives and to promote just social relations, where justice means something more than simply aggregate wealth-maximization.” ^{Footnote 74}

Writing in conjunction, Alexander and Peñalver build upon this theory. Together, they advance a conception of community based on the Aristotelian insight into the inherently social nature of human beings, arguing that dependence on others is integral to human flourishing. ^{Footnote 75} Their theory envisages plural modes of human flourishing and stresses the need for individuals to have the capacity to choose and deliberate carefully upon their options in life. ^{Footnote 76} They contend that all individuals are equally entitled to the means necessary for human flourishing and that the mutual recognition amongst individuals of the value of flourishing requires those with the means to flourish to share their resources with those who would otherwise lack the necessary material resources. ^{Footnote 77} Such obligations are determined by the needs of others and can require disproportionate contributions from some in society. ^{Footnote 78}

Alexander and Peñalver address the appropriate role of the state in their theory, acknowledging that social interdependence, and the relationship between human flourishing and community, do not necessarily mean that the state should enforce the resulting individual obligations. ^{Footnote 79} They note that in early societies, local communities could supply human beings’ needs, and that such provision continues in modern society. ^{Footnote 80} However, they characterise private redistribution as insufficiently reliable to secure access for all to the material goods that are required for human flourishing, saying, “… at least since the rise of modern capitalism, the uncoerced actions of private entities have never been sufficient to supply all members of society with access to all of the resources necessary for them to have the opportunity to develop the capabilities necessary for human flourishing.” ^{Footnote 81} They invoke Aquinas’ discussion of theft to justify their conclusion that the state should be not only empowered, but required, to qualify individual property rights in order to secure human flourishing, extending to the compulsory sharing of surplus property. ^{Footnote 82}

(C) Aquinas in Human Flourishing Property Theory—Summary

Overall, three important direct uses of Aquinas’ property theory can be identified in modern human flourishing property theory. First, Aquinas’ practical justification of private possession is invoked to explain a property virtue—the virtue of industry—while also bolstering the claim that industry, and with it efficiency, is not the exclusive or paramount property virtue. Second, Aquinas’ arguments on theft and superflua have been relied upon to justify governmental redistribution of property as a means of enforcing owners’ social obligations, underpinned by the ultimate objective of securing of human flourishing for all individuals within a community. Relatedly, Aquinas’ views on theft have been used to justify broader consideration of necessity as a defence to, or a mitigating factor in respect of, property offences such as theft and trespass. More generally, at the conceptual level, Aquinas’ property theory has been relied upon to support the view, central to progressive property theory, that private possession of property is only legitimate subject to its consistency with securing the needs of all individuals.

(A) Efficiency and Industry

Peñalver used Aquinas’ practical justification of private possession of property to argue that industry is a virtue that should shape land-use decision-making, and that the law should seek to encourage, but is not the exclusive or primary property virtue. This reliance highlights the fact that Aquinas viewed private ownership as subject to the more important need to secure material sustenance for all men. For the modern property theorist, Aquinas’ approach, and Peñalver’s use of it, persuasively demonstrates that a commitment to efficiency, and to the benefits of coordination in respect of land-use, does not necessarily require a non-pluralistic approach to property’s values, nor does it require an absolute commitment to securing efficiency above all else. Rather, efficiency (or in Peñalver’s terms, industry) can be understood as one important aspect of property’s goals that must be balanced with competing values and aims realised through, or affected by, property.

This insight, prompted by Peñalver’s use of Aquinas’ practical justification of private ownership and its relationship to common use, is helpful in bridging the divide that has arisen between information theorists, who prioritise efficiency, simplicity and transparency in property law, and progressive property theorists, who contemplate a significant degree of contextual decision-making in property law. ^{Footnote 84} As illustrated by Peñalver’s approach, and his reliance on Aquinas for support, progressive property theorists can and do champion efficiency as an important goal of property alongside other values, recognising its coordination benefits. ^{Footnote 85} Similarly, some information property theorists regard efficiency, as well as predictability and simplicity, as a means to other ends (e.g., human flourishing). ^{Footnote 86}

Furthermore, Peñalver’s approach, building on Aquinas’ focus on the coordination and efficiency benefits of private possession, provides a strong response to criticisms levied against the contextual nature of the progressive perspective and its attendant information costs. ^{Footnote 87} Insofar as efficiency, industry and clarity are values that form part of a contextual approach to property, the need for sensitivity to information costs, and for predictability and stability in property law, are capable of being captured by such an approach. Progressive property theories can give weight to the benefits of efficiency and low information costs, not as ends in themselves, but as important values that may help to secure progressive values through the use and management of land.

Where disagreement between these perspectives hardens is concerning how reliable legal rules are at realising property’s ends, and how often such rules should be reconsidered or displaced. While progressive property theorists are unwilling to accept that efficiency should be allowed to trump fairness in individual cases, or to impede the realisation of other progressive goals in respect of property, information theorists argue that ‘property rules’ should not be jettisoned in favour of more complex ‘governance rules’ lightly. ^{Footnote 88} Such theorists give priority to simple, readily comprehensible property rules as a reliable means of securing a well-functioning property system that operates fairly in most cases. Accordingly, Peñalver’s reliance on Aquinas’ account of the coordination benefits of private possession of property remind us that the division between progressive property theorists and at least some prominent information theorists centres on their different views about the appropriate means of property law.

(B) The Redistribution Debate

As already noted, human flourishing property theory argues that the state has the power and duty to compel redistribution, and regards such a power as justified based on the need to secure equal opportunities for human flourishing to all individuals. ^{Footnote 89} Aquinas’ discussion of property, particularly his treatment of theft and superflua, is relied upon within human flourishing property theory to support this conclusion. Two aspects of this reliance will be considered here: first, the significance of Aquinas’ general subordination of private ownership to common use; second, the status of governmental redistribution in Aquinas’ property theory.

Human flourishing property theory, and progressive property theory more generally, are at their core driven by the view that ownership is qualified by the needs of others, including non-owners, and cannot confer powers that impede the ability of all individuals to live equally in a secure and dignified way in society. ^{Footnote 90} The scope of owners’ rights depends upon their broader impact on social relations. ^{Footnote 91} Ownership is understood to entail duties and not to confer absolute freedom, because the legal protection and enforcement of property rights necessarily disempowers those lacking such rights. These basic ideas echo the key tenet of Aquinas’ theory of property, according to which freedom in respect of private property is restricted by the basic requirement that external goods be available to support the lives of all equally valuable individuals through securing their material sustenance. ^{Footnote 92} Thus the foundational premise of human flourishing property theory, and of progressive property theory more generally, is strongly supported by Aquinas’ theory of property.

Furthermore, Aquinas’ approach reminds us that private property can be limited even where private ownership is recognised as a necessary legal institution. As already discussed, Aquinas conceived of private possession of property as an addition of human reason to the law of nature forming part of the ius gentium, which comprised principles created by human reason through direct derivation from the law of nature. Academics have divided substantially over whether the ius gentium is properly classified as part of the law of nature or human law. ^{Footnote 93} While detailed consideration of that long-running debate is beyond the scope of this paper, it is submitted that whichever view is adopted, for Aquinas the ius gentium was made up of principles closely derived from, and closely connected to, the law of nature. Consequently, Aquinas clearly rooted property as an institution, as distinct from any particular set of legal rules concerning property, in natural law. ^{Footnote 94} At the same time, he identified clear limits to private ownership, treating it as subordinate to the urgent material needs of others in society. In this way, Aquinas’ theory provides a useful reminder that even where private ownership is naturalised, whether at a constitutional level, through human rights instruments, or otherwise, it can be subjected to the needs of those who do not possess property. The obligations and responsibilities of owners do not disappear simply because private ownership is recognised as derived from natural law, since the scope of owners’ exclusive rights is determined by the primary need to secure the material sustenance of all equally valuable individuals.

Turning from this broad conceptual coherence between progressive property theory and Aquinas’ thinking on property to consider the detail of Thomistic property theory highlights the need to consider further the respective roles of private redistribution and public redistribution and the relationship between these two ways of achieving progressive property goals. This reflection is prompted by the fact that there is some disagreement amongst scholars on whether Aquinas’ theory of superflua can be translated into a justification for redistribution of privately held property by the state.

The dominant interpretation of Aquinas’ property theory, which is employed in human flourishing property theory, is that it does translate into an argument for governmental redistribution of privately held property. ^{Footnote 95} For example, Andrew Lustig argues that the use of Aquinas’ theory to support redistribution of property by government has a long and well-developed tradition in Catholic social and political theory, which employed and extended Aquinas’ theory in justifying property, even as such theory moved in the direction of natural individual rights. ^{Footnote 96} Furthermore, he contends that such a translation is necessary in the context of modern, non-agrarian economies. ^{Footnote 97} Finally, he argues that Aquinas himself contemplated distributive decisions being made by rulers. ^{Footnote 98} Robert Dyson adopts a similar view, asserting that while Aquinas left the distribution of superflua up to individual owners, today, “…his argument would no doubt find expression as an argument in favour of progressive or redistributive taxation.” ^{Footnote 99} Marcus Lefébure contends that in light of Aquinas’ views on superflua, “the government should enjoy a reserve right to ensure that individuals do in fact exercise their stewardship of common resources for the common good, including a right to supervene when necessary in order to redistribute property more fairly.” ^{Footnote 100} Thus according to Lefébure, Aquinas regarded responsibility for ensuring the proper use of property as being divided between the individual and the State. ^{Footnote 101} This interpretation coheres with several aspects of Thomistic property theory: with Aquinas’ argument that the parameters of property are set by the need to ensure that the basic needs of all are met; with his identification of obligations for owners to share privately held property to secure this end; and with his argument that theft does not, properly speaking, occur where a person takes from another’s superfluous property to secure such basic needs. Overall, the interpretation of Aquinas’ property theory as supporting governmental redistribution of property is plausible, particularly insofar as it is true to the prioritisation of use for material sustenance over private property within that theory.

However, a competing interpretation of Aquinas’ views on governmental redistribution merits some consideration by human flourishing property theorists given the priority of virtue within their approaches to property. Paul J. Weithman contends that for Aquinas, property is common only insofar as owners have a duty to independently use superflua to help those in need, on the basis of their individual judgment, and accordingly that this argument does not justify governmental redistribution. ^{Footnote 102} Weithman argues that it is impossible to replace this individual administration of superflua with redistribution by the State, as this would limit the scope for individuals within society to engage in virtuous activity, which was central to Aquinas’ political theory. ^{Footnote 103} In particular, he contends that the public administration of superflua would limit opportunities for developing and exercising the virtues of practical wisdom, justice, mercy, and liberality that are prioritised by Aquinas. ^{Footnote 104}

This interpretation of Aquinas’ property theory closely reflects Aristotle’s defence of private property. Aristotle argued, “[t]here is the greatest pleasure in doing a kindness or service to friends or guests or companions, which can only be rendered when a man has private property.” ^{Footnote 105} According to Aristotle, part of the purpose of private possession of property was to facilitate private redistribution of resources, which led him to object to common property, since “[n]o one, when men have all things in common, will any longer set any example of liberality, or do any liberal action; for liberality consists in the use which is made of property.” ^{Footnote 106} David Lametti explains this symbiosis between private property and virtue as follows:

Accordingly, from this perspective, private property is understood to assist in the development of virtue, for example by enabling voluntary redistribution to the needy.

This means that the interpretation of Aquinas’ theory relied upon in human flourishing property theory, although widely supported, is contested. More significantly for the purposes of this article, Weithman’s interpretation highlights the need to consider the balance between public and private redistribution within human flourishing property theory, and to do so bearing in mind the prioritisation of the facilitation of virtuous activity by individuals. Weithman’s view of the problematic nature of governmental redistribution is overly extreme, since, as Alexander and Peñalver acknowledge, the relationship between public and private redistribution is not an all or nothing matter—private redistribution can still occur within a regime of compelled redistribution. ^{Footnote 108} The extent to which private redistribution can occur in such a context may depend on the intensity of governmental compulsion, so the two are undoubtedly related, but not mutually exclusive. Nonetheless, Weithman’s interpretation of Aquinas’ views on property is worthy of some consideration within progressive property theory, since it focuses attention on the need to think carefully about the consequences that flow from recognising ownership obligations for public and private actors respectively, and on the extent to which those obligations should be reflected in the content and/or enforcement of legal rules. It further suggests the need to consider in greater detail the functional impact of the choice of legal means in light of the values driving progressive property theory—whether owners’ obligations should be implemented by requiring direct, private action by owners, e.g., in redistributing property or refraining from enforcing property rights, or whether the identification of legally enforceable ownership obligations is primarily a means of justifying public law measures that limit or redistribute property. Again, these approaches are not mutually exclusive—owners can have individual obligations that they directly implement, whether through voluntary redistribution or through non-enforcement or qualified enforcement of private rights, as well as obligations that are implemented through direct governmental action. However, these two approaches, while they might be used to achieve the same ends, do so by allocating the burden of identifying and fulfilling ownership obligations to different actors: in the case of voluntary redistribution, to the owner him or herself; in the case of non-enforcement or qualification of private rights, to the owner and in the event of dispute, the courts; and in the case of direct governmental action, to a combination of legislative, executive and judicial action. While there is undoubtedly overlap between these three approaches, they empower different actors to different degrees. From the perspective of the development of progressive property theory, it is important to reflect upon these different allocations of responsibility with a view to identifying the most effective means of achieving a progressive outcome in the context of particular property issues or disputes.

Alexander and Peñalver themselves do not purport to provide definitive answers to these difficult questions, although they clearly acknowledge that both public and private redistribution have important roles to play in human flourishing property theory ^{Footnote 109} and they identify the importance of carefully calibrating the use of the law to enforce owners’ obligations ^{Footnote 110} . They further recognise the complexity of appropriately balancing individual freedom and collective decision-making against the backdrop of facilitating human flourishing. ^{Footnote 111} Thinking further about the implications of the choice between moral and legal obligations, and between public and private law obligations, for the realisation of the goals of human flourishing property theory, or indeed other progressive property perspectives, may require greater engagement with the different nuances of those theories as applied in public and private law contexts. While those spheres may be inseparable at the level of identifying the normative values of property law ^{Footnote 112} , they are separable as distinct, albeit related and at times overlapping, legal means of achieving those values.

Although the insights of legal realism, identifiable at the root of much progressive property theory, correctly emphasise the close relationship between public and private law, including the important role of the state in both legal contexts ^{Footnote 113} , that fact does not mean that there are no relevant differences between public and private law measures, considering the goals of progressive property. Public law mechanisms largely place the onus for identifying what is required to fulfil ownership obligations on the State, which it may do for example through imposing restrictions on individual property rights that administrators and/or courts may be called upon to enforce in the event of non-compliance (depending on the design of the measure). Private law mechanisms are likely to give greater agency to individual owners in the first instance to define and satisfy their obligations qua owner, and to give residual power to courts to resolve disputes between private actors, albeit against the backdrop of any overlapping public law measures. Accordingly, owners may have different degrees of agency in the fulfilment of their moral and legal obligations qua owners, depending on whether a predominantly public or private law approach is adopted to ensure the fulfilment of ownership obligations. Furthermore, the choice of legal means will affect the ‘property audience’ affected by a change in legal rules. ^{Footnote 114} While systemic changes to private law rules may have a wide impact, at least some public law measures have a narrower reach, and accordingly are likely to have limited adverse implications for the day-to-day mutual recognition of, and respect for, property rights that is foundational to the private law system of property.

A full exploration of those differences is beyond the scope of this article, which aims as a preliminary matter to encourage greater attention to be paid within progressive property theory to the appropriate balance between voluntary and legally enforced fulfilment of owners’ obligations, and to prompt more fine-grained analysis of the differences between the various types of legal mechanisms for enforcing owners’ obligations against the backdrop of the goals of progressive property theory. ^{Footnote 115} The answers to these difficult foundational questions will, consistently with the general approach of progressive property theory, be contextually determined, and furthermore, will be contingent on local factors. They will likely vary depending on the issue being addressed and the broader social, economic and legal culture in which it arises. The degree of trust in government and the values and bonds of affected communities will also impact significantly upon the balance between private and public redistribution that is appropriate to secure progressive goals in any given context, as well as legal and broader cultural attitudes towards public and private legal regulation. ^{Footnote 116}

All of this means that progressive property theory, in its implementation, will necessarily differ between, and within, jurisdictions, and will change over time with shifts in legal, social and economic culture. Although the values of progressive property may be identifiable in relatively stable terms, its means will (consistent with its emphasis on contextual decision-making) be variable, although not necessarily unpredictable. ^{Footnote 117} While the various approaches for implementing ownership obligations identified in this article—voluntary action, private law enforcement, public law enforcement—are not suggested to be mutually exclusive or hermetically sealed from each other, attending to their nuanced differences, including their empowering effects, is important for the future development of progressive property theory, in order to ensure that it can effectively achieve outcomes consistent with its goals. It may also be relevant for the development of responses to criticism of progressive property theory, since the degree of power conferred on the courts to adjudicate on a case-by-case basis (a much-criticised aspect of progressive property theory) may vary depending on the design of legal measures that are intended to secure the fulfilment of ownership obligations, and depending on the balance between public and private legal mechanisms.

(C) Necessity and Property Offences

A final qualification is required concerning the use by some human flourishing property theorists of Aquinas’ arguments concerning theft to support arguments for the normative and legal plausibility of an expanded defence of necessity to property offences such as theft and trespass. As discussed in Part I, Aquinas clearly argued that the sin of theft was not committed where property was taken from its possessor to satisfy the urgent and evident need of the dispossessor for material sustenance. Accordingly, Aquinas’ views on theft are consistent with imposing narrow limits on the enforceability of exclusive claims to material goods where those claims conflict with the urgent and basic needs of others for sustenance. ^{Footnote 118} However, Aquinas set strict parameters for the exercise of the limited right to self-help that he recognised, in order to secure the practical benefits that he saw could be created by property.

As noted above, Aquinas’ treatment of theft and superflua was invoked by Peñalver and Katyal to support their argument that necessity should be capable of being considered either as a defence to, or a mitigating factor in respect of, property offences in a broader range of circumstances than traditionally recognised by courts in the US. ^{Footnote 119} They argued that economic needs, as well as physical needs, should trigger consideration of necessity, and that the focus should not be merely on basic sustenance. However, Peñalver and Katyal did not address the limited and extreme circumstances in which Aquinas envisaged an individual’s needs generating an entitlement to take privately possessed property from another. As noted above, Aquinas regarded the distribution of superflua as a matter for the judgment of the owner, except in circumstances where access to material goods was urgently needed to secure an individual’s survival in the absence of any alternative. Therefore, Aquinas’ approach does not offer direct support for relaxing or removing the requirement of established urgency of need, or for expanding the scope of any entitlement of those meeting that threshold beyond access to basic material goods required for physical survival. This restricts the usefulness of his theory for any proposed expansion of the defence of necessity designed to achieve broader progressive ends.