Post by Samuel Beswick, Frank Knox Memorial Fellow, SJD candidate, Harvard Law School
At last Wednesday’s Private Law Workshop, Rebecca Stone presented new experimental evidence on whether, and under what conditions, people regard promises as generating obligations to keep them. Based on a study of some 780 subjects, Mischkowski, Stone and Stremitzer find that people regard the issuance of a promise in and of itself, and the fact of another’s reliance on a promise, as each carrying binding force. They further find an additive effect when the two conditions co-exist—i.e., when a promise is relied upon.
The authors set up a simple vignette study: imagine you are a prospective buyer and have told a seller that you will purchase a product from them for $100 when you get back into town. Depending on the version of the vignette (six versions were randomly assigned to the pool of subjects), you either promised to make the purchase or you stated an intention to buy the product but disavowed any promise to do so. You (the buyer) are told that the seller—in the spirit of Monty Python’s shopkeeper who is alternately rude and polite—either believed your promise, did not believe your promise, or was not sure (again, depending on the version of the vignette, randomly assigned). Finally, you are told that, prior to your return you happen to learn that another seller is prepared to sell you the same product for $85. Subjects are then asked whether they will buy from the original seller or instead buy from the other seller at the lower price.
Mischkowski, Stone and Stremitzer find evidence of three motivations for people’s decisions to keep their promises. First, regardless of whether they made or disavowed a promise to the original seller, subjects who were told that the seller had credited their assertions that they were planning to buy from the seller were more inclined to buy from the original seller than subjects who were told that the seller had not credited or had doubted their assertions (an expectations per se effect). Second, subjects who made a promise, as opposed to those who disavowed any promise, were more inclined to buy from the original seller regardless of what they were later told about the seller’s expectations (a promising per se effect). Third, subjects were most inclined to keep their promises when they had promised to purchase from the original seller and when they were told that the seller was expecting them to purchase the product (an interaction effect).