Understanding Capital Combinations Entails an Understanding of the Concepts of Complementarity and Substitutability

According to Lachmann, though the capital-stock is heterogeneous, it is not amorphous. The various components of the capital stock stand in sensible relationship to one another because they perform specific functions together. That is to say, they are used in various capital combinations. If we understand the logic of capital combinations, we give meaning to the capital structure and, in this way, we are able to design appropriate economic policies or, even more importantly, avoid inappropriate ones.

Understanding capital combinations entails an understanding of the concepts of complementarity and substitutability. These concepts pertain to a world in which perceived prices are actual (disequilibrium) prices, in the sense that they reflect inconsistent expectations, and in which changes that occur cause protracted visible adjustments. Capital goods are complements if they contribute together to a given production plan. A production plan is defined by the pursuit of a given set of ends to which the production goods are the means. As long as the plan is being successfully fulfilled, all of the production goods stand in complementary relationship to one another. They are part of the same plan. The complementarity relationships within the plan that may be quite intricate and no doubt involve different stages of production and distribution. 

Substitution occurs when a production plan fails (in whole or in part). When some element of the plan fails, a contingency adjustment must be sought. Thus some resources must be substituted for others. This is the role, for example, of spare parts or excess inventory. Thus, complementarity and substitutability are properties of different states of the world. The same good can be a complement in one situation and a substitute in another. Substitutability can only be gauged to the extent that a certain set of contingency events can be visualized. There may be some events, such as those caused by significant technological changes, that, not having been predictable, render some production plans valueless. The resources associated with them will have to be incorporated into some other production plan or else scrapped; they will have been rendered unemployable. This is a natural result of economic progress which is driven primarily by the trial-and-error discovery of new and superior outputs and techniques of production. What determines the fate of any capital good in the face of change is the extent to which it can be fitted into any other capital combination without loss in value. Capital goods are regrouped. Those that lose their value completely are scrapped. That is, capital goods, though heterogeneous and diverse, are often capable of performing a number of different economic functions.

—Peter Lewin, “Hayek and Lachmann,” in Elgar Companion to Hayekian Economics, ed. Roger W. Garrison and Norman Barry (Cheltenham, UK: Edward Elgar Publishing, 2014), 169-170.