Staunchly opposed to an all‐​volunteer military, which must pay its soldiers market wages, Gen. Westmoreland proclaimed that he did not want to command “an army of mercenaries.” One of the commission members immediately shot back with a question: “General, would you rather command an army of slaves?” That penetrating query was posed by Milton Friedman, a diminutive (he stood only 5 feet 3 inches tall) giant among 20th‐​century scholars. Were he still alive — he died in 2006 — Friedman would celebrate his 100th birthday on July 31.

Bald and bespectacled, Friedman looked every part the University of Chicago economics professor that he was. During his long tenure at that celebrated institution, he produced a stream of cutting‐​edge research on consumer behavior, on the role of money, and on the history of U.S. and British monetary policy. The impressive quantity, quality, and importance of this research without doubt places Friedman among the top two or three economists of the past century.

Friedman, indeed, is one of the few scholars whose receipt of the Nobel Prize in Economics — which he received in 1976 — did at least as much to bestow prestige on that award as that award did to bestow prestige on him. (The first Nobel Prize in Economics wasn’t awarded until 1969.) Friedman’s stupendous scholarly achievements alone justify commemoration of the centenary of his birth.

But at least as important as Friedman’s scholarship was his lucid and energetic public advocacy of limited government and free markets. He explained with unmatched clarity how a modern economy’s complexities, nuances, and dynamism almost always thwart even the best‐​intentioned efforts by government officials to intervene into markets.

In a scene from the opening episode of his successful 10‐​part 1980 PBS series “Free to Choose,” Friedman held in his hand an ordinary pencil. Looking into the camera, and speaking without a script, he explained that a pencil — so seemingly simple — requires for its production the knowledge and labors of millions of people from around the world.

Some workers cut down the trees; other workers make the chainsaws used to cut down the trees; yet other workers make the steel used to manufacture the chainsaws; and yet other workers specialize in mining the iron ore used to make the steel. Still other workers mine the graphite to make the “lead” for the pencil, while many others work in factories to make the yellow paint that commonly adorns pencils, while still other workers perform the many tasks required to produce the rubber for each pencil’s eraser.

Just to list the number of different, highly specialized jobs that must be performed to produce a commonplace pencil would take volumes. Few of these workers know each other, and none of them knows how to do any more than one or two of the countless jobs that must be done if we are to be well‐​supplied with pencils.

Friedman explained how free‐​market prices, along with the lure of profit and the fear of loss, guide entrepreneurs, firms, and workers from across the globe to produce just the right amounts of wood, graphite, paint, erasers, and the many other parts of pencils.

No government commissars are involved. There’s no central plan for the production of pencils. Yet we have high‐​quality pencils in abundance and for sale at low prices. What’s true for pencils, of course, is true also for more complex items such as automobiles, electric lighting, MRI machines, and on and on — that is, for nearly every good commonly found in modern industrial society.

No one equaled Friedman’s skill at explaining how free markets succeed at coordinating the activities of legions of individuals to produce the goods and services that we today take for granted. Likewise, no one equaled his skill at explaining how government regulators are typically oblivious to the complexity of the coordination achieved by markets. Being oblivious, regulators’ interventions too often obstruct this market coordination.

Note that Friedman would heartily agree with President Obama that no one prospers in today’s economy exclusively through his or her own individual efforts. Where Friedman would disagree — and disagree strongly — is with Obama’s suggestion that the main source of help that each of us gets from others is government. While government might supply some necessary pieces, such as highways and law courts, the vast bulk of what society supplies for each person’s sustenance and success comes not from government but from the ongoing private efforts of millions of individuals acting in free markets.

Friedman’s brilliant use of the pencil, like his reply to Gen. Westmoreland, reveals the great talent Friedman had for cutting to the heart of the matter in ways easily understood by almost everyone.

Revealing the awesome complexity of the humble pencil makes clear that no government regulators can ever hope to know enough about the entire economy to regulate it as well as it is regulated by free‐​market forces. Calling the military’s seizure of years of labor from young men “slavery” reveals the fact that draftees — like plantation slaves of old — are forced against their will to work for others and on terms dictated by others.

Friedman’s response to Gen. Westmoreland is evidence also of Friedman’s lifelong commitment to the cause of human freedom. Not only was conscription economically inefficient (as Friedman showed in academic research), it was also an affront to the values of a free society.

In a free society government is kept as small and as constrained as possible, charged with doing only those few tasks that are widely believed to be doable only by government — tasks such as building roads and supplying national defense. All other tasks are left to the creative forces of the free market. And in doing those few tasks, Friedman maintained, the freedom and dignity of every individual must always be respected.

Americans of my generation likely first encountered Friedman through his regular column in Newsweek, which ran from 1966 through 1984. Each of these essays cogently made the case for reducing the reach of government. In making this case, Friedman consistently defied conventional stereotypes. He was, he always insisted, not a conservative but, rather, a liberal — a true liberal, in the original meaning of that term.

Being a classical liberal, Friedman vigorously championed not only economic freedoms but also freedoms emphasized by many folks on the political left, such as freedom of speech and of assembly. It speaks volumes of Friedman’s principles that he, the owlish and dedicated scholar so beloved by many establishment conservatives for his support of free enterprise, was among the most vocal and unwavering opponents of the “war on drugs.” He insisted, with characteristic wit, that “the government has no more right to tell me what goes into my mouth than it has to tell me what comes out of my mouth.” Truly great men and women are rare. What they all share is the courage of their convictions, the wisdom to distinguish cant from reality, and enormous energy and ability in working to make the world a better place. Milton Friedman was one such genuinely great man.