Quincy Jones once told me something that I have never forgotten.

He said that when he was coming up as a young musician in New York, there was a kid in his circle who played clarinet and saxophone. A smart kid. A careful kid. A kid who could sit in any room and, within minutes, understand exactly how everything worked. He went to Juilliard. He played with the great Stan Getz—side by side, night after night, in the Henry Jerome Orchestra—and somewhere along the way, the other musicians figured something out about him that he was only beginning to figure out about himself.

He was the one you went to when the numbers didn't add up.

Between sets, while the rest of the band disappeared into the green room, this kid was doing the bookkeeping. Running the ledgers. Filing the tax returns for his bandmates. He understood money the way the others understood music—intuitively, structurally, as a system with its own logic and rhythm. And somewhere in those years of playing beside Stan Getz — one of the greatest jazz voices of the twentieth century — he made a discovery about himself that changed the course of American history.

That kid was Alan Greenspan. And today, he is gone. He was 100 years old.

Economist Alan Greenspan around 1974. Wally McNamee/Corbis—Getty Images

Greenspan was a good musician. But his true gift was economics. So he put down the saxophone, picked up an economics textbook, and eventually became one of the world’s most powerful financial voices.

Jones, of course, went on to become one of the greatest music impresarios in history. Two young men from the same rooms, the same bandstands, the same late nights. One would go on to conduct the global........

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