If this was the issue in the famous 'two Cambridges' controversy,
then it has long since been resolved in favor of this side of the
~tlantic." Physical capital, too, is best viewed as a force, not directly
observable, that we postulate in order to account in a unified way for certain
things we can observe: that goods are produced that yield no immediate
benefit to consumers, that the production of these goods enhances labor
productivity in future periods, and so on