In my youth it was said that what was too silly to be said may be sung. In modern economics it may be put into mathematics. - Ronald Coase

The limit to the size of the firm is set where its costs of organizing a transaction become equal to the cost of carrying it out through the market. This determines what the firm buys, produces, and sells. As the concept of transaction costs is not usually used by economists, it is not surprising that an approach which incorporates it will find some difficulty in getting itself accepted. We can best understand this attitude if we consider not the firm but the market.

But a theory is not like an airline or bus timetable. We are not interested simply in the accuracy of its predictions. A theory also serves as a base for thinking. It helps us to understand what is going on by enabling us to organize our thoughts. Faced with a choice between a theory which predicts well but gives us little insight into how the system works and one which gives us this insight but predicts badly, I would choose the latter, and I am inclined to think that most economists would do the same.

What is studied is a system which lives in the minds of economists but not on earth. I have called the result “blackboard economics.” The firm and the market appear by name but they lack any substance. The firm in mainstream economic theory has often been described as a “black box.” And so it is.