Does Trust Promote Generosity?

Both of trust and generosity have been considered as important factors to promote cooperation (Yamagishi 1998, Nesse 2001). Some researchers argue that trust plays a significant role in assessing quality and trustworthiness of unknown others. On the other hand, generosity is defined as a tendency to forgive defects or failures of partners (Exline & Baumeister 2000, McCullough 2008). However, these two cooperation promoting-traits appear to be incompatible. Trust helps us to assess partner’s trustworthiness, which may lead to a withdrawal from inappropriate relationships. On the other hand, generosity helps us to forgive partner’s mistakes, implying that we make a commitment in spite of partner’s failures. Therefore, the question is: Are these two traits really compatible? And if so, how do we have developed these two seemingly contradicting traits?

Here, we aim to clarify the puzzling relationship between trust and generosity by using an agent-based modeling. We adopt trust game as a basic building block and then incorporate two further elements into our model. One is related to heterogeneous agents in terms of abilities to fulfill donor’s expectation. The other element is related to partner choice, commitment (repeated trust games with the same partner) and an exit. Trust is thus formulated as selective strategies in the context of partner choice, whereas generosity is defined as forgiveness of partner’s failures in the context of commitment relationship. We carry out the set of computer simulation experiments to assess the viability of several strategies.

Our first result is: without reasonable trustful strategies, more generous strategies cannot be viable. Furthermore, we find that as group size increases, trust level also goes up, leading to the prevention of degenerating generosity. These two results clearly indicate that trust can promote generosity. Put it differently, there exists a coevolution mechanism of trust and generosity in our social world.