Super Thinking: Upgrade Your Reasoning and Make Better Decisions with Mental Models

by Gabriel Weinberg

Another way to internalize externalities is through a marketplace. Ronald Coase won the Nobel Prize in economics in 1991 in part for what has become known as the Coase theorem, essentially a description of how a natural marketplace can internalize a negative externality. Coase showed that an externality can be internalized efficiently without further need for intervention (that is, without a government or other authority regulating the externality) if the following conditions are met: Well-defined property rights Rational actors Low transaction costs When these conditions are met, entities surrounding the externality will transact among themselves until the extra costs are internalized. If you recall the Boston Common example, the externality from overgrazing was internalized by setting a limit on the number of cows per farmer (regulation). There were no property rights though. The Coase theorem holds that instead of limiting the cows, another solution would have been to simply divide the grazing rights to the commons property among the farmers. The farmers could then trade the grazing rights among themselves, creating an efficient marketplace for the use of the commons.