The 20th century produced a pantheon of brilliant urban thinkers and planners. Some built, some mostly wrote, some did both. Some did better than others at translating their ideas into reality. But one way or another, we are living with the consequences of their vision:

Ebenezer Howard's "garden cities," Le Corbusier's "radiant city," Frank Lloyd Wright's "Broadacre City"--even Lewis Mumford's unrealized dream of regional planning--all of them represent the baseline for anyone who wants to create a modern urban revival.

But there's a dirty little secret that nearly all the legendary members of the urbanist Hall of Fame have in common. They really didn't like cities very much--at least the ones they lived in and knew about. Wright and Le Corbusier considered the urban industrial metropolis of their time to be dirty, smelly, noisy, crowded and vastly inferior to the skyscraper-and-park cities they could conjure up on their drawing boards. Mumford acquired a reputation as one of the most passionate urbanists of all time, but what he really admired most was the medieval village, where, as he saw it, people could be in touch with nature every moment of the day. The more he saw of mid-century Manhattan, the unhappier he became.

The purpose of this column, however, isn't to focus on this set of individuals, but rather to celebrate the accomplishments of the one great 20th-century urbanist who really loved cities--loved them for their noise, their energy, their complexity, for the sheer quantity of life they managed to generate.

As you may have guessed, I'm referring to Jane Jacobs. This year marks the 40th anniversary of her masterpiece, "The Death and Life of Great American Cities." Happily, Jacobs is alive and well, still writing and lecturing from her home in Toronto at age 85. Even more happily, her work has become a readily available classic, still on the shelves in almost every good bookstore in the country.

Nobody, of course, would be foolish enough to claim that Jane Jacobs' wisdom has become settled doctrine in the world of city planning and urban design. The battles she ignited are still being fought, and not always with success for her side. But to a remarkable extent, she set the agenda in 1961, and it remains about where she set it. It's only a slight exaggeration to say that contemporary urban thought is a series of footnotes to Jane Jacobs.

When she wrote "Death and Life," downtown renewal in American cities consisted largely of the destruction of two-story commercial structures, their replacement by large office towers, and the creation of huge windswept plazas in which no one congregated.

Now, at the very least, most of us realize that empty plazas are no urban adornment. But the person who first taught us that was Jane Jacobs, insisting that expert opinion was wrong: that successful cities are built out of street life--people of all sorts, coming and going at all hours, working, playing and gossiping on the same sidewalks, forming the casual relationships upon which trust can grow.

"Life begets life," Jacobs wrote. Busy streets are safe streets. Empty streets are dangerous. That's no more than simple common sense now. But it was heretical 40 years ago.

"Death and Life" was prescient in so many ways that one short column couldn't possibly acknowledge them all. Jacobs argued for the reclaiming of seedy industrial waterfronts for recreational purposes. "The waterfront itself," she argued, "is the first wasted asset capable of drawing people at leisure."

She warned against single-purpose zoning and described mixed-use development as the foremost weapon in rebuilding a city neighborhood. Today that is accepted wisdom not only among New Urbanists but in the planning department of virtually every big American city.

Perhaps even more important--and certainly less heeded--was Jacobs' corollary warning that financial capital and physical rebuilding will not restore a community whose social life has been depleted. "It is fashionable," Jacobs wrote, "to suppose that certain touchstones of the good life will create good neighborhoods--schools, parks, clean housing and the like. How easy life would be if this were so!... There is no direct, simple relationship between good housing and good behavior..." and "important as good schools are, they prove totally undependable at rescuing bad neighborhoods." Billions of wasted dollars and limitless human disappointment could have been averted by a public willingness to face up to those Jacobean truths.

Nobody is right about everything, though, and I would argue--although I doubt she would agree--that she was wrong about at least a couple of things. Based on her experiences as an activist in New York's Greenwich Village, Jacobs felt that no organized urban neighborhood of fewer than 75,000 people could be large enough to wield meaningful clout in the political structure of a huge city. It seems to me that this was more true of New York in the 1960s than of cities in general. Communities smaller than Jacobs' prescribed minimum have fought City Hall and won numerous times in the largest cities in the past 40 years.

Moreover, she was utterly disdainful of metropolitan regionalism. She described a region as "an area safely larger than the last one to whose problems we found no solution." She thought that regional alliances and consolidation of political power were no answer to the difficulties either of cities or of the suburbs sprouting up around them. It seems to me that if regionalism is a difficult and often unpalatable choice, it may be the only realistic one left for quite a few of the struggling metropolitan areas in this country.

But if Jacobs was wrong about a couple of things, she was breathtakingly right about so many--and she was able to express her insights in a casual, ironic, unpretentious way that makes her as much a pleasure to read now as she was in the 1960s, when I first encountered her in college.

And that suggests one more crucial lesson about Jane Jacobs worth paying some attention to: She was an amateur. Jacobs was by training neither a planner nor an architect nor an urban historian nor anything else that might suggest uncommon learning in her field. She was a newspaper reporter from Scranton, Pennsylvania, who moved to New York with her husband and children in the early postwar years, settled into a Greenwich Village apartment, took an interest in Village affairs, read the urban policy literature, traveled around the country to check on other cities, and emerged with a fund of common sense that no formal degree or professional credential could possibly have given her.

It is a silly question to ask who will be the Jane Jacobs of the 21st century. No one will be; she is as original and irreproducible as anyone who has ever written about cities and community. But it may be reasonable to observe that, when and if someone makes literate and persuasive sense out of the next round of urban problems and challenges, it won't be someone with a long series of titles and degrees surrounding his name. It will be someone with the virtues of an intelligent and curious amateur.

In the decade or so since New Urbanism exploded onto the local policy and planning scene, it has generated millions of words of analysis and prescription detailing how intelligent design can restore the sense of community and rootedness that city life has lost in the past half century. Some of this literature is readable and useful; some of it is not.

But none of it has seemed more sensible and appealing to me than "How Cities Work," Alex Marshall's new book of urban reporting and commentary. Marshall shares with Jane Jacobs one characteristic: He is an amateur--a longtime Virginia newspaper reporter whose methods consist largely of watching, reading, traveling and thinking.

Marshall is both sympathetic to New Urbanism and critical of it. His criticisms are simple and cogent ones. Essentially they boil down to this: Transportation is destiny. Communities are creatures of the transportation systems that grow up around them. American downtowns and Main Streets of the early 20th century were compact and vibrant because people walked there or came in on trains and moved in and out of stations twice a day. It's fine to be nostalgic for the physical intimacy of the old-time small town or gritty city, but it's impossible to have it in a society dependent for its mobility on the automobile.

Therefore, Marshall argues, there is something inescapably false about New Urbanist efforts to re-create a small-town America of picket fences, front porches and sidewalk gossip in developments constructed as enclaves along freeways and virtually inaccessible except by car. "Bringing back the street," he concludes, "is not possible unless we bring back the forms of transportation that made it essential."

Marshall would actually like to see those old urban forms return to life. He likes the idea of compact downtowns friendly to pedestrians and fed by fast and efficient public transportation. He is merely making the point that if we are to create such a societal change in the coming century, we will need to think through all the trade-offs and sacrifices it will entail. We will have to return to old ways of getting around. We will not be able to revive the neighborhoods of the past simply by redesigning streets and houses.

Reading Alex Marshall and rereading Jane Jacobs in quick succession leaves a similarly bracing feeling: Their books amount to a cold bath of common sense whose implications an urban cheerleader might just as soon avoid, but whose logic is ultimately difficult to escape.

This is not to say that Alex Marshall is the next Jane Jacobs. That would be unfair to both of them. It's merely a reminder of something we might all stop and ponder. In urban policy, as in most other fields, smart amateurs are worth paying attention to. They have a way of keeping us all in touch with reality.