Ronald Coase, who died this week at the age of 102, was one of the greatest economists of the 20th century. His impact on academic thought and public policy is incalculable.

In 1991, Coase won the Nobel Memorial Prize in Economic Sciences in part for a theorem he set out in a 1960 article that is, by a large margin, the most cited law-journal paper of all time. The Coase theorem produced a revolution in both thought and public policy.

His target was the great British economist Arthur Cecil Pigou, who contended that if a polluter is emitting smoke, and thus causing injury, the best response is to make the factory owner pay for the injury or to impose a corrective tax.

Coase said Pigou failed to see “the reciprocal nature of the problem.” Suppose that a very noisy factory is causing legal injury to a doctor operating next door. Under Pigou’s approach, the factory should be required to pay damages to the doctor. But Coase pointed out that we could also make the doctor bear the cost. His central insight was that if people can bargain with one another, and if it isn’t costly for them to do so, it just doesn’t matter who is required to pay: People will negotiate their way to the efficient solution. This is the Coase theorem in a nutshell.

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