Economists of every persuasion have long agreed that the basis of the capitalistic system is, quite simply, privately owned capital: money that comes from accumulated savings and is used to finance investment. Now, however, worried policymakers and students of the system have begun to debate the causes and implications of a historic development. For the first time in more than half a century, the U.S., like some other industrial economies, faces an acute shortage of the capital that is needed to create new goods, profits, public services and—by no means least—jobs.
The...