For the last two decades, there has been a growing argument that “social capital” derived from human relationships has an influence on various aspects of social phenomena. In many such studies, it is pointed out that social capital has two aspects social relationships as “network” and “trust” associated with such relationships. However, there has been a tendency for them to be discussed separately and they have not been integrated into one concept of social capital.
In this paper, we would like to define the ‘tie’ of human relationships and ‘strength of tie’ among the component concepts of social capital in a formal manner, and try to define the ‘trust’ mechanism as a function that maps ‘one's act counting on other people's actions’ into its feasibility. We will then explore the empirical credibility of such formalization by analyzing survey data.
In the following two sections, we will make clear related problems. First, we try to distinguish the ‘feasibility of one's acts which count on other people's actions’ from the probability of other people's action. In our view, one will never calculate an expected utility using the probability of other people's actions in everyday life. He/she will only judge whether his/her act counting on other people's actions is feasible or not. In the next section, we will distinguish the ‘trust’ mechanism from the ‘confidence’ mechanism according to Luhmann. We see their difference as a difference in domain of feasibility that each mechanism concerns.