Encouraging cooperation: revisiting solidarity and commitment effects in prisoners' dilemma games

Pre-play discussion consistently increases cooperation in dilemma interactions. Most explanations of this "cheap-talk" effect are based on either commitment or group solidarity effects. Because discussion about the upcoming dilemma allows participants to make promises and creates group solidarity, the 2 explanations are often confounded. This paper aims to clarify past results by having participants engage in an unrelated discussion prior to a dilemma interaction. We find that solidarity effects can be induced by minimal group categorizations, but are relatively weak. Discussions involving consequential but unrelated coordination tasks are shown to prime cooperative norms and increase cooperation with both in-group and out-group members. Our findings suggest that cheap talk may work for even cheaper reasons than previously thought.