Jacobs, in 1969: an ordinary mom who set out to protect the neighborhood. Photograph by Elliott Erwitt / Magnum and John J. Burns Library, Boston College

I got to talk to Jane Jacobs once, toward the end of her life, an interview that is mentioned, in its properly Lilliputian proportion, in Robert Kanigel’s new biography, “Eyes on the Street: The Life of Jane Jacobs” (Knopf). She was one of three people I have met in a lifetime of meeting people who had an aura of sainthood about them, the others being Iona Opie, the British folklorist who collected children’s rhymes, and I. F. Stone, the independent American journalist. What they had in common was a sort of radiant self-reliance. They could say an obvious thing—that children are citizens of another country, that all governments lie—with the conviction that comes from having really found it out. They spoke for many, because they thought for themselves. Iona Opie made hanging around schoolyards to find small variants in jumping-rope rhymes seem essential to understanding humanity, and Izzy Stone made you feel unpatriotic for not printing your own biweekly page of political commentary. The ability to radiate certainty without condescension, to be both very sure and very simple, is a potent one, and witnessing it in life explains a lot in history that might otherwise be inexplicable—for instance, how a sixteen-year-old girl could lead the French Army to victory.

Jane Jacobs’s aura was so powerful that it made her, precisely, the St. Joan of the small scale. Her name still summons an entire city vision—the much watched corner, the mixed-use neighborhood—and her holy tale is all the stronger for including a nemesis of equal stature: Robert Moses, the Sauron of the street corner. The New York planning dictator wanted to drive an expressway through lower Manhattan, and was defeated, the legend runs, by this ordinary mom.

Even after the halo above the saint’s head fades, however, we have to make sense of the ideas that rattled around inside. I. F. Stone’s independence remains thrilling to every blogger, or should, but his attempts in retirement to reconcile Jefferson and Marx seem less inspiring than impossible. Now, in the year of Jane Jacobs’s centenary, with the biography out there, along with a new collection of her uncollected writings, “Vital Little Plans: The Short Works of Jane Jacobs” (Random House), and an anthology of conversations between her and various friends, “Jane Jacobs: The Last Interview and Other Conversations” (Melville House), it seems fair to pay her the compliment of taking her seriously—to ask what exactly she argued for, and what exactly we should think about those arguments now.

Her admirers and interpreters tend to be divided into almost polar opposites: leftists who see her as the champion of community against big capital and real-estate development, and free marketeers who see her as the apostle of self-emerging solutions in cities. In a lovely symmetry, her name invokes both political types: the Jacobin radicals, who led the French Revolution, and the Jacobite reactionaries, who fought to restore King James II and the Stuarts to the British throne. She is what would now be called pro-growth—“stagnant” is the worst term in her vocabulary—and if one had to pick out the two words in English that offended her most they would be “planned economy.” At the same time, she was a cultural liberal, opposed to oligarchy, suspicious of technology, and hostile to both big business and the military. Figuring out if this makes hers a rich, original mixture of ideas or merely a confusion of notions decorated with some lovely, observational details is the challenge that taking Jacobs seriously presents.

When Lewis Mumford reviewed Jacobs’s “The Death and Life of Great American Cities” in these pages, in 1962, it was under the now repugnantly condescending title “Mother Jacobs’ Home Remedies.” But it conformed to the image of Jacobs that, with her help, had become prevalent: that of an ordinary Greenwich Village mom, in sensible bangs and oversized glasses, out to protect the neighborhood from the destructive intrusions of alien big shots.

Unsurprisingly, this turns out to be a caricature. Kanigel, who has found the right tone for his subject, light but serious, introduces us to the young Jane Butzner, as she was born, in 1916. His portrait of growing up in the Butzner family, in Scranton, Pennsylvania, is hugely attractive. Her parents were the kind of old-fashioned “nonconformists’’—not exactly bohemian, and certainly not radical—who seem to have mostly vanished from American life, the kind that Kaufman and Hart wrote plays about. Confident in their social status, not least because they descended from a secure background (there were Daughters of the American Revolution in the family tree), they indulged their daughter’s eccentricities, clearly seeing them as part of her character, her “spunk.” A skeptic of authority from the beginning, she staged a grade-school rebellion against having to pledge to brush your teeth—she wasn’t against the brushing, just the coerced promise—that led to her being briefly expelled. She believed that authority could be laughed away, a powerful notion for a provocateur to take through life. The young Jacobs also held long imaginary conversations with the Founding Fathers, dismissing Jefferson’s abstractions in order to talk to the more practical-minded Ben Franklin, who “was interested in nitty-gritty, down-to-earth details, such as why the alley we were walking through wasn’t paved, and who would pave it,” as she recounted to an interviewer. Scranton was a thriving capital of the coal industry in those days, but it quickly fell on harder times, and the regular evocation, in her work, of thriving rather than stagnant cities surely echoes her sense of the fine little town’s rise and fall.

Like so many rebellious, gifted American girls impatient with ordinary paths—Louisa May Alcott was of the same kind—she went on to avoid higher education and become a miscellaneous journalist, while still quite young. Throughout her life, she kept the swinging style of that profession, along with the journalist’s habit of letting a broad and brilliant view do the work of patient statistical investigation. Though an ambitious theorizer, she is at her best as an observer: she leaps plenty, but she looks first.

Jacobs found her vocation quickly but her subject very late. She spent several years working for a magazine called Amerika, published by the U.S. State Department for distribution in the Soviet Union. Only in the mid-nineteen-fifties did she begin writing about urban issues and architecture, first for Architectural Forum and then for Fortune, which offered a surprisingly welcoming home to polemics against edifice-building. She married an equally cheerful, nonconformist architect, Robert Jacobs, and they moved—just before the first of their three children was born—into a house at 555 Hudson Street, an address that, for certain students of American originals, has attained the status of Thoreau’s cabin at Walden.

Though Jacobs was later portrayed as an engaged, block-party mom, Kanigel reveals that she was much too busy writing and working to do much real street living; her shopping was mostly done by phone. It was her more abstract experience of large-scale urban renewal elsewhere, particularly in Philadelphia, under the then much praised Edmund Bacon, that really kindled her growing indignation about what was happening to cities.

A paragraph heading in a piece for Fortune summed up her new belief: “The smallness of big cities.” Big cities thrived, she wrote, because they were full of healthy micro-villages; small ones became overdependent on one or two businesses, turning into plantation towns with company stores (as Scranton had been too dependent on coal). She became notorious for attacking Lincoln Center, then under construction. A cynosure of everything forward-looking and ambitious in urban design, it represented to her, almost alone, the apotheosis of the “super blocks” that destroyed the “hurly-burly” of city life. Anti-modernist at a time when few progressives dared to be, she was invited to a symposium on cities at Harvard in 1956, and did a Ruby Keeler, going up to the lectern an unknown and coming back to her seat a star.

It was against this background of established notoriety that Jacobs published, very much under the guidance of the editor Jason Epstein, “The Death and Life of Great American Cities.” The book is still astonishing to read, a masterpiece not of prose—the writing is workmanlike, lucid—but of American maverick philosophizing, in an empirical style that descends from her beloved Franklin. It makes connections among things which are like sudden illuminations, so that you exclaim in delight at not having noticed what was always there to see.