Social capital is a real, measurable resource — and it's been shrinking

Putnam borrows the term social capital to describe something concrete: the networks of relationships and the norms of reciprocity and trust that let people get things done together, from organizing a carpool to holding a functioning democracy together. Like financial capital, it can accumulate or be depleted.

His case is that it's been depleting in America since roughly the 1960s and 70s, across nearly every measure he can find — club membership, church attendance, union rolls, volunteering rates — even as the population and wealth of the country grew. The famous image that gives the book its title: Americans bowl about as much as ever, but league bowling, where you show up weekly and know your teammates, has cratered in favor of casual, solitary bowling.

The generational pattern is stark: each cohort born after roughly 1940 has been measurably less civically engaged than the one before it, a pattern too consistent to be coincidence.

Takeaway: connection between people is an economic-style resource, and by Putnam's account, America has been running a decades-long deficit.