The third and most fundamental premise is that instructions for working with raw materials are inherently different from other economic goods. Once the cost of creating a new set of instructions has been incurred, the instructions can be used over and over again at no additional cost. Developing new and better instructions is equivalent to incurring a fixed cost. This property is taken to be the defining characteristic of technology.
Paul M. Romer, "Endogenous Technological Change," Journal of Political Economy 98, no. 5, Part 2 (Oct., 1990): S71-S102.
