Three years after World War II drew to a close, a young professor at MIT published "Foundations of Economic Analysis." Its mathematical approach to economics would revolutionize the profession. And its author, Paul Samuelson, would go on to earn many awards and honors, culminating in 1970, when he won the Nobel Prize in economics—the second year it was awarded. Samuelson died on Sunday at the age of 94.

His influence has been profound, but the mathematization of economics has been a mixed blessing. The downside is that the...