Psychological ownership – whether a thing feels like it is Mine – has been studied by philosophers for centuries and by psychologists dating back to James (Reference James1890). Theorists argue that the driving predictor of whether people feel psychological ownership for a thing t is the degree to which t is associated with the self (Beggan, Reference Beggan1992; Belk, Reference Belk1988; Morewedge, Reference Morewedge2021; Weiss, Reference Weiss2022). They posit that factors within the stimulus, context, and judge that facilitate or inhibit the association between a thing and the self determine which objects feel “Mine” and when objects will feel “Mine” (Atasoy & Morewedge, Reference Atasoy and Morewedge2018; Shu & Peck, Reference Shu and Peck2011; Weiss & Johar, Reference Weiss and Johar2016). People are more likely to feel psychological ownership for an object such as a coffee mug with their university logo than a plain mug, for instance, because the university logo facilitates the association between the mug and self (Dommer & Swaminathan, Reference Dommer and Swaminathan2013). This literature also identifies the driving predictors of the perception of shared or collective ownership (“Ours”) as the degree to which a group of individuals (e.g., coworkers, students, neighbors) (1) share a sense of “us” and (2) form an association between the group and the thing (e.g., Pierce & Jussila, Reference Pierce and Jussila2010; Verkuyten & Martinovic, Reference Verkuyten and Martinovic2017). We dub these interpersonal theories because they pertain to judgments made from the first-person perspective of the actor (Morewedge, Reference Morewedge2021).

Boyer proposes a theory of how ownership is evaluated from the perspective of an observer. Boyer's theory complements earlier work by predicting when observers perceive a thing as owned, by whom, and how strong is the ownership connection (“Theirs”). Drawing on resource competition and cooperative models of resource sharing, Boyer identifies cues that observers may use in interpersonal judgments of the ownership felt by agent A toward thing t (contiguity, modifications, interaction, defense). Some of these cues overlap with cues used in intrapersonal judgments. Others are new.

Comparisons between these intrapersonal and interpersonal perspectives raise three new questions about the evaluation of ownership. An obvious first question is the degree to which intrapersonal and interpersonal judgments are distinct. Many of the factors identified by Boyer, such as contiguity, use, and defense, already are factors assumed to be essential to intrapersonal judgments of psychological ownership. An important difference between psychological ownership from the perspective of an observer versus an actor pertains to the conditions under which each should ensue. Boyer predicts that observers' intuitions about ownership and ownership violations should only ensue when a thing t can be considered a rivalrous good. In contrast, intrapersonal theories of individual or group psychological ownership suggest and have shown that psychological ownership for a thing develops whether it is rivalrous or not (e.g., a home vs. a public park). Research is needed to discern if Boyer's theory identifies new facets of a single process by which people evaluate ownership for self and for others, or if people do use different processes to evaluate what they own and what others own. This work has the potential to contribute to the considerable literature on judgments of self and others (Alicke, Dunning, & Krueger, Reference Alicke, Dunning and Krueger2013; Pronin, Reference Pronin2008).

A related second set of questions pertains to the circumstances in which intrapersonal and interpersonal judgments will not align, and implications of these misalignments. Observers' judgments, as captured through Boyer's model, should accurately predict their own behavior (e.g., whether an observer would try to separate thing t from agent A or would help agent A to protect thing t) but may not predict the behavior of the observed agent (e.g., whether agent A will respond aggressively to an attempt to separate thing t from that agent). Similarly, the agent's judgment, as captured by extant research on psychological ownership, should accurately predict the agent's but may not predict the observer's behavior.

Consider the consequences for negotiation in a case where two people, Yasser and Yitzhak, dispute who owns a plot of land bordering their homes, and a third observer, Bill, serves as an arbiter. Yasser and Yitzhak would each evaluate their ownership of the disputed land using the intrapersonal model. Bill would use Boyer's interpersonal model. Yasser and Yitzhak may also use Boyer's interpersonal model to assess each other's ownership, or some variation on the intrapersonal model. These different perspectives may lead Yasser and/or Yitzhak to underestimate how strong is the other's psychological ownership for the land. Bill may underestimate this for the both of them. Their underestimation may increase the likelihood that the parties will attempt to negotiate their ownership claims, but also reduce the likelihood that negotiation will resolve their dispute. All parties may overestimate the likelihood of a resolution and underestimate the difficulty others will have making concessions.

A third question is how different processes of evaluating ownership for self and others informs (and should inform) law and policy regarding property rights and resolutions of legal and political disputes. Are the sticks in the bundle of property rights associated with legal ownership (i.e., accessing, controlling access, modifying, profiting, transferring rights, destroying; Morewedge, Reference Morewedge2021), grounded in the evaluations of ownership made by actors or observers? Do and should the courts treat these evaluations as complementary, are courts guided by one perspective, or do and should courts treat intrapersonal and interpersonal evaluations as substitutes? How do these evaluations play out in business or political negotiations and disagreements about disputed land, objects, and ideas, and how might they be used together to help resolve those disputes?

We are excited by this shift in perspective from self to other and its potential to enrich and inform a scientific understanding of ownership and approaches to resolve disagreements about what is Mine, Ours, and Theirs.