Boyer's article presses the field to address oft-overlooked questions about ownership psychology. He provides compelling evidence against ad-hoc social norm accounts of ownership, and proposes a novel minimalist model wherein ownership psychology is the result of interactions between cognitive systems dedicated to cooperation and competition.

In this commentary, we challenge Boyer's model by discussing ways that the self might be a more likely cognitive foundation of ownership intuitions (Belk, Reference Belk1988; Locke, Reference Locke and MacPherson1978[1690]). Under an extended-self account, people extend themselves to their objects and then subsequently regard their property as parts of themselves (Belk, Reference Belk1988; Locke, Reference Locke and MacPherson1978[1690]). Ownership has deontic normative implications (see target article, sect. 8.2.2) because transgressions against property are viewed in the same light as any other (moral) transgression against someone's body. For instance, work shows young children and adults reason in similar ways about violations to people's bodies and property (Van De Vondervoort & Friedman, Reference Van De Vondervoort and Friedman2015; Van de Vondervoort, Meinz, & Friedman, Reference Van de Vondervoort, Meinz and Friedman2017). Other work further supporting this account shows that self-owned objects are privileged in human cognition (e.g., Cunningham, Vergunst, Macrae, & Turk, Reference Cunningham, Vergunst, Macrae and Turk2013; Gelman, Manczak, & Noles, Reference Gelman, Manczak and Noles2012) in ways similar to other kinds of self-relevant stimuli (e.g., Symons & Johnson, Reference Symons and Johnson1997). For instance, children preferentially track and remember their own property over others’ property (Cunningham et al., Reference Cunningham, Vergunst, Macrae and Turk2013; Gelman et al., Reference Gelman, Manczak and Noles2012), but individuals with differences in self-representation, such as those diagnosed with autism spectrum disorder, do not tend to show these behaviors (e.g., Grisdale, Lind, Eacott, & Williams, Reference Grisdale, Lind, Eacott and Williams2014; also see Hartley & Fisher, Reference Hartley and Fisher2018).

At the core of this extended-self account are principles that signal the strength and boundaries of ownership relations – control and investment. Let us first consider control. Just as people freely control parts of themselves (e.g., their arms), they are thought to freely control their property (Belk, Reference Belk1988). This means that establishing control over an entity often leads it to be viewed as property (e.g., Belk, Reference Belk1988; Furby, Reference Furby1978; Morewedge, Reference Morewedge2021; Rudmin & Berry, Reference Rudmin and Berry1987). For instance, psychological ownership can be signaled simply by controlling an entity like moving a cup in a restaurant (e.g., Kirk, Peck, & Swain, Reference Kirk, Peck and Swain2018). This principle also explains judgments regarding ownership boundaries or what can/cannot be owned (see target article, sect. 9.3). For example, agents described as autonomous are viewed as less ownable because their autonomy conflicts with owners’ abilities to control them (Starmans & Friedman, Reference Starmans and Friedman2016; also see Espinosa & Starmans, Reference Espinosa and Starmans2020, for related work with children). As Starmans and Friedman (Reference Starmans and Friedman2016) posit, this reasoning could explain intuitions about slavery. Next, we consider investment. As Boyer suggests, ownership is often attributed after personal investment because it causes property to be incorporated into the self (e.g., Belk, Reference Belk1988; Locke, Reference Locke and MacPherson1978[1690]). However, investment should be construed as broader than Boyer's discussion of physical labor, as it can include emotions, ideas, and (non-labor) time. Indeed, the psychological ownership literature suggests that many of these types of investments are sufficient to trigger feelings of ownership (see, e.g., Peck & Luangrath, Reference Peck and Luangrath2023, for an overview).

Taken together, these principles also provide insight into why sometimes ownership is contested, such as Boyer's squatter example (target article, sect. 8.3). Intuitively, a squatter's ownership status is ambiguous as the principles of control and investment do not lead to clear-cut judgments: On one hand, the squatter could be the owner as they have invested labor in the property and by doing so demonstrated control over it. But on the other hand, the constructs of investment and control are abstract and difficult to measure. Namely, how much of the “self” the squatter has seemingly invested as opposed to the initial owner cannot be precisely calculated by our intuition. Differences in these intuitive calculations then lead to inconsistency in supporting the squatter's claim. Adding to this intuitive noise, under a legal framework, the property's ownership status is also ambiguous: Ownership was not formally transferred to the squatter. Thus, we contend that noise in people's judgments about ownership should simply be taken as evidence that people are responding to noisy input, and not evidence against specific intuitive principles. Indeed, in other domains of reasoning, researchers have found that intuitive principles are often imprecise (e.g., Keil, Reference Keil2010) and conflict with non-intuitive explanatory frameworks like scientific (e.g., Gelman & Legare, Reference Gelman and Legare2011; Shtulman & Legare, Reference Shtulman and Legare2020) and legal ones (Sommers, Reference Sommers2021).

A core question we have not yet addressed is what predicts when people choose to respect ownership once it is established. As Boyer (target article, sect. 8.2) points out, people sometimes do not respect others’ ownership rights. We propose that by extending oneself onto property, the property is then subsumed into the owner's overall welfare. Specifically, people likely engage in a cost–benefit analysis which allows them to predict and explain the contexts where ownership is upheld. That is, people would expect agents to transgress if the agents’ cost–benefit analysis is net positive. For instance, people might predict a transgression if the perceived benefit of obtaining a stolen resource is particularly high, or if the cost to the owner (or themselves) is low. Related to this point, children believe it is more acceptable to take resources from the rich to give to the poor than the reverse (Echelbarger, Roberts, & Gelman, Reference Echelbarger, Roberts and Gelman2022; Essler & Paulus, Reference Essler and Paulus2021) likely because the perceived cost to the rich is lower than the poor's benefit. This account also explains when agents will heed ownership. Namely, when the cost of transgressing is too high, or when the benefit to the transgressor is too low, there is no motive to violate owners’ rights and ownership should be heeded. Importantly, these cost–benefit analyses do not rely on competitive or cooperative factors and could be computed by a domain-general mechanism interacting with ownership information.

In sum, it seems to us that the self is arguably a more minimalist explanation for ownership intuitions than one that requires coordination among cooperative and competitive systems. Nonetheless, a pressing direction for future work will be to tease apart which cognitive system(s) is/are necessary and sufficient to explain the heart of ownership psychology.