Tuesday, June 23, 2026

Instability, A Problem For The Theory Of Supply And Demand

General Equilibrium Theory (GET) is the most rigorous and most developed version of the theory of supply and demand. More than half a century ago, economists discovered that GET does not support the just so stories many economists still tell. (Experimental economists have validated Scarf's example of instability.)

Franklin Fisher was an authority on this topic.

"Yet the very power and elegance of equilibrium analysis often obscures that it rests on a very uncertain foundation. We have no similarly elegant theory of what happens out of equilibrium, of how agents behave when their plans are frustrated. As a result, we have no rigorous basis for believing that equilibria can be achieved or maintained if disturbed. Unless one robs words of their meaning and defines every state of the world as an 'equilibrium' in the sense that agents do what they do instead of doing something else, there is no disguising the fact that this is a major lacuna in economic analysis.

Nor is that lacuna only important in microeconomics. For example, the Keynesian question of whether an economy can become trapped in a situation of underemployment is not merely a question of whether underemployment equilibria exist. It is also a question of whether such equilibria are stable. As such, its answer depends on the properties of the general (dis)equilibrium system which macroeconomic analysis attempts to summarize. Not surprisingly, modern attempts to deal with such systems have been increasingly forced to treat such familiar macroeconomic issues as the role of money." -- Franklin M. Fisher. 1987. Adjustment processes and instability. In J. Eatwell, M. Milgate, P. Newman, The New Palgrave: A Dictionary of Economics. Macmillan.

As far as I know, although some interesting work has been done, this gap still exists.

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