Games of pure mutual interest require players to coordinate their choices withoutbeing able to communicate. One way to achieve this is through team-reasoning,asking ‘what should we choose’, rather than just assessingone’s own options from an individual perspective. It has been suggestedthat team-reasoning is more likely when individuals are encouraged to think ofthose they are attempting to coordinate with as members of an in-group. In twostudies, we examined the effects of group identity, measured by the‘Inclusion of Other in Self’ (IOS) scale, on performance innondescript coordination games, where there are several equilibria but nodescriptions that a player can use to distinguish any one strategy from theothers apart from the payoff from coordinating on it. In an online experiment,our manipulation of group identity did not have the expected effect, but wefound a correlation of .18 between IOS and team-reasoning-consistent choosing.Similarly, in self-reported strategies, those who reported trying to pick anoption that stood out (making it easier to coordinate on) also reported higherIOS scores than did those who said they tended to choose the option with thelargest potential payoff. In a follow-up study in the lab, participants playedeither with friends or with strangers. Experiment 2 replicated the relationshipbetween IOS and team-reasoning in strangers but not in friends. Instead,friends’ behavior was related to their expectations of what theirpartners would do. A hierarchical cluster analysis showed that 46.4% ofstrangers played a team reasoning strategy, compared to 20.6% of friends. Wesuggest that the strangers who group identify may have been team reasoning butfriends may have tried to use their superior knowledge of their partners to tryto predict their strategy.

In a recent article in this journal, Duijf claims to have proved that team reasoning can be viewed as a payoff transformation. His formalization mimics team reasoning but ignores its essential agency switch. The possibility of such a payoff transformation was never in doubt, does not imply that team reasoning can be viewed as a payoff transformation, and makes no sense in a game in which payoffs represent players’ utilities. A theorem is proved here that a simpler and more intuitive payoff transformation can mimic any theory that predicts what strategies players will choose in a well-defined game.

This paper examines two strands of literature regarding economic models of cooperation. First, payoff transformation theories assume that people may not be exclusively motivated by self-interest, but also care about equality and fairness. Second, team reasoning theorists assume that people might reason from the perspective of the team, rather than an individualistic perspective. Can these two theories be unified? In contrast to the consensus among team reasoning theorists, I argue that team reasoning can be viewed as a particular type of payoff transformation. However, I also demonstrate that many payoff transformations yield actions that team reasoning rules out.

Team reasoning is thought to be descriptively and normatively superior to the classical individualistic theory of rational choice primarily because it can recommend coordination on Hi in the Hi-Lo game and cooperation in Prisoner's Dilemma-type situations. However, left unanswered is whether it is rational for individuals to become team members, leaving a gap between reasons for individuals and reasons for team members. In what follows, I take up Susan Hurley's attempt to show that it is rational for an individual to become a team member. I argue that her account fails to show that becoming a team member is necessary to gain the advantages of coordination in Hi-Lo games or cooperation in Prisoner's Dilemma-type situations, and that individuals will often fare better reasoning as individual agents than as members of a team. I argue further that there is a more general problem for team reasoning, specifically that the conditions needed to make it rational for a team member to employ team reasoning make becoming a team member unnecessary.

The game theoretic notion of best-response reasoning is sometimes criticized when its application produces multiple solutions of games, some of which seem less compelling than others. The recent development of the theory of team reasoning addresses this by suggesting that interacting players in games may sometimes reason as members of a team – a group of individuals who act together in the attainment of some common goal. A number of properties have been suggested for team-reasoning decision-makers’ goals to satisfy, but a few formal representations have been discussed. In this paper we suggest a possible representation of these goals based on the notion of mutual advantage. We propose a method for measuring extents of individual and mutual advantage to the interacting decision-makers, and define team interests as the attainment of outcomes associated with maximum mutual advantage in the games they play.

If group members aim to fulfil a collective obligation, they must act in such a way that the composition of their individual actions amounts to a group action that fulfils the collective obligation. We study a strong sense of joint action in which the members of a group design and then publicly adopt a group plan that coordinates the individual actions of the group members. We characterize the conditions under which a group plan successfully coordinates the group members’ individual actions, and study how the public adoption of a plan changes the context in which individual agents make a decision about what to do.