A prototypical vintage capital model of economic growth is developed, where the decision to replace old technologies with new ones is modeled explicitly. Technological change is investment specific. Depreciation in this environment is an economic , not a physical concept.

This is a specific investigation of the importance of technological change specific to new investment goods for postwar U.S. aggregate fluctuations. A growth model that incorporates this form of technological change is calibrated to U.S. data and simulated, using the relative price of new...