The evidence of laboratory experiments of behavioral economists shows that individuals behave reciprocally. These data put into question the pure self-interest thesis of human motivation of the homo oeconomicus model and call for alternative models. Focusing on the explanation of reciprocal behavior in Trust Games, this article proposes two directions that economists and other social scientists might want to consider in order to establish a more solid foundation for economic theory. First, it presents models that economic theorists developed to explain (...) the laboratory evidence of reciprocal behavior. It highlights that all of these models subscribe to the Humean view that desires are at the source of any human motivation and suggests an alternative Kantian model where reasons have the capacity to motivate human action. Second, it emphasizes that a supplementary examination of the social background conditions would illuminate the analysis of the findings because of the connection between the 'local' and society-wide demands of reciprocity. (shrink)