Do People Keep Socially Unverifiable Promises?

Previous research has suggested that communication and especially promises increase cooperation in laboratory experiments. This has been taken as evidence for internal motivations such as guilt aversion or preference for promise keeping. The original goal of this paper was to examine promises under a double blind payoff procedure to test the alternative explanation that promise keeping was due to external influence and reputational concerns. We find no evidence that communication increases the overall level of cooperation in our double blind experiment. However, our results are due in part to the high level of cooperation that we observe, leading us to conduct additional single blind conditions. Ultimately, we find no evidence that communication or payoff procedures impact aggregate cooperation.