Part I

Growth accounting has a remainder. After measured capital and labor have made their contribution, part of the change in output is left to total factor productivity. Economists have never mistaken that residual for a single physical substance. It gathers changes in technique, organization, quality, utilization, measurement, and much else that the specification does not separately identify.

It may also conceal changes in the conversion of energy into useful work. A heterodox line running from Frederick Soddy through Nicholas Georgescu-Roegen to Robert Ayres insists that production cannot be understood as though physical throughput were an incidental purchase. Useful-work models sometimes account for historical output unusually well. That result is an invitation to causal inquiry, not a verdict that energy was the missing variable all along.

The distinction matters because an accounting category can remain stable while the machinery beneath it changes. If computation makes new kinds of physical throughput economically usable, inherited measures may register the consequence without naming the conversion. Part I follows that possibility from Soddy's physical economics through Solow's residual to Wrigley's account of England's escape from organic constraint. Its claim is not that energy completes a theory of value. It is that no account of production can be complete while the work performed by its physical economy remains invisible.