Although William J. Baumol, who recently died at 95, was not widely known beyond the ranks of economists, all Americans are living with, and policymakers are struggling with, “Baumol’s disease.” It is one reason brisk economic growth is becoming more elusive as it becomes more urgent. And it is a disease particularly pertinent to the increasingly fraught health care debate.

Born in the Bronx, Baumol spent his teaching career at Princeton and NYU but remained an aficionado of New York opera, and when in 1962 the Metropolitan Opera’s orchestra went on strike, Baumol sought an explanat...