Three families of social capital concepts are discussed: (fa1) trust, (fa2)
ease of cooperation, and (fa3) network. In the language of game theory, so
cial capital is the excess propensity to play cooperative solutions in pris
oners' dilemma games. The three families lead to different definitions, and
thus to different measurement methods. Some measures are theory-near, whil
e others are easy-to-use proxies. It is shown that all definitions and meas
ures are related. The 'social capital dream' is that all definitions try to
catch aspects of the same phenomenon, so that all measures tap the same la
tent variable. It is discussed whether this dream is likely to come true.