While Americans were deeply engaged in communal affairs for the first two-thirds of the 20th century, they retreated from one another and communal life in the last third of that century. Historically, there have been periods of collapse and renewal of civic engagement, so it is possible that the trends in the latter part of the 20th century can be reversed.

Drawing upon records of organizations and public opinion polls, Putnam demonstrates the decline of communal life in the US. As a result, social capital, or “social networks and the norms of reciprocity and trustworthiness that arise from them” (19), has declined with negative consequences for American society.

Social capital benefits both individuals and the community: A distrustful society is not as efficient, for example. Ideally, the positive consequences of social capital, such as cooperation and trust, should be maximized, while the negative consequences, such as sectarianism and corruption, should be minimized. Putnam distinguishes between inclusive or bridging forms of social capital and exclusive or bonding forms. Bridging forms are more valuable to society because they generate broader identities and reciprocity (23) but tie individuals weakly to one another. Bonding forms are beneficial for individuals but tend to bolster in-group loyalty and out-group antagonism.