The Economic Significance of the Heterogeneity of Capital Is That Each Capital Good Can Only be used for a Limited Number of Purposes

All capital resources are heterogeneous. The heterogeneity which matters is here, of course, not physical heterogeneity, but heterogeneity in use. Even if, at some future date, some miraculous substance were invented, a very light metal perhaps, which it was found profitable to substitute for all steel, wood, copper, etc., so that all capital equipment were to be made from it, this would in no way affect our problem. The real economic significance of the heterogeneity of capital lies in the fact that each capital good can only be used for a limited number of purposes. We shall speak of the multiple specificity of capital goods.

--Ludwig M. Lachmann, Capital and Its Structure (Kansas City: Sheed Andrews and McMeel, 1978), 2.