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 question always is, will it pay to bring an extra exchange transaction under the organizing authority? At the margin, the costs of organizing within the firm will be equal either to the costs of organizing in another firm or to the costs involved in leaving the transaction to be “organised” by the price mechanism. Business men will be constantly experimenting, controlling more or less, and in this way equilibrium will be maintained. This gives the position of equilibrium for static analysis.

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.

Markets are institutions that exist to facilitate exchange, that is, they exist in order to reduce the cost of carrying out exchange transactions. In an economic theory which assumes that transaction costs are nonexistent. markets have no function to perform, and it seems perfectly reasonable to develop the theory of exchange by an elaborate analysis of individuals exchanging nuts for apples on the edge of the forest or some similar fanciful example. This analysis certainly shows why there is a gain from trade, but it fails to deal with the factors which determine how much trade there is or what goods are traded.