The mat below the porch door is where Chicago paperboys are taught to aim their papers. With practice, my brother Noah, who had a route in the early 1970s, was able to cover the few square blocks of his Hyde Park route in half an hour or so. One morning, however, an older customer came out in his bathrobe and asked my brother to place the paper inside the porch.

This necessitated getting off the bike.

“It’ll be worth your while,” the man said.

At Christmas, my brother discovered it was: The man left a $20 tip, larger by far than any other Noah received.

The old professor was Milton Friedman, and my brother was one of the millions to learn the power of incentive from him in his lifetime. After the economist died at 94 last autumn, a sort of “Friedmania” overcame the world — like President Ford’s, Friedman’s death made him larger. Tonight, a PBS biography, “The Power of Choice: The Life and Ideas of Milton Friedman,” makes clear exactly how Friedman changed the way everyone — not just Americans, or economists — view day-to-day life.

The first thing this excellent program reminds us is what Friedman and his Chicago friends were up against. Between the 1940s and 1970s, America’s political leaders really did believe in John Maynard Keynes’s old rule that “a large extension of the traditional functions of government” was necessary in the new era. In those days, too many economists (even GOP economists) believed they should manage the economy almost hour by hour, using any number of devices that have since proven to be perverse or destructive.

After the Englishman died, John Kenneth Galbraith, a nearly-Englishman from Canada, preached the Keynes message to the Yahoos in America. “The Power of Choice” contains a wonderful clip of Ambassador Galbraith on a talk show sometime in the 1970s, archly telling the audience that “wage and price controls are an indispensable part of any economic policy that this country can have.”

Friedman, as this program demonstrates, attacked such thinkers first of all on the economic plane. His “Permanent Income Hypothesis” demonstrated that citizens don’t respond so much to their government’s short-term behavior as to their own assessments of what will happen to themselves economically during the course of their lifetimes. If voters or taxpayers expected government — the man on the porch, as it were — to change its mind frequently, they would be less likely to change behavior on the basis of its offers. An even more important contribution from Friedman came on the monetary side. Friedman and his partner, Anna Schwartz, showed with their landmark monetary history that the Great Depression was caused by government failure to recognize deflation —not the failure of the stock market.

But Friedman also battled successfully on the political plane, including presidents from Ford forward. Friedman judged President Nixon the most intelligent but found that President Reagan understood his arguments best — in part, perhaps, because Reagan was old enough to have been educated before Keynes took hold. Friedman’s own famous documentary, “Free To Choose,” aired in 1980, the year Reagan ran for the presidency.

A million viewers crowded before TV screens to watch Friedman reach for the “STOP” button at the printing presses at the United States Mint to show how you checked inflation. They also watached him sail across Hong Kong harbor to illustrate the possibilities of globalization. Bob Chitester, one of the producers of “Free To Choose,” also worked on “The Power of Choice,” so it would make sense for this new documentary to boost the old one. Still, one cannot help but sense that this show’s claim that “Free To Choose” helped to turn the nation away from Jimmy Carter is true.

The biggest quarrel one can have with “The Power of Choice” is that it tends to give a foreshortened view of history. The celebratory tone gets a little irritating, almost Catskill-like. Watching it, you get the impression that Friedman single-handedly invented free-market economics or taught Tallinn, Estonia, that trade was good. In fact — as even one opponent, Galbraith, points out on the air — many of the ideas for which Friedman fought were well understood in the 18th century. Tallinn knew how to trade long before Friedman was born — trading was part of its identity as an open port city and member of the Hanseatic League.

But it is Friedman’s admirers who paint him too grandly. Milton himself was simply what he was: the best of all possible professors, one who reminded the world of what it knew as common sense before Keynesianism made it forget. Thanks in part to Friedman, that knowledge is with us again, safely inside the porch door.

Ms. Shlaes is a visiting senior fellow at the Council on Foreign Relations and a Bloomberg columnist.