Mention that a biography is unauthorized and all sorts of presumptions come into play: This is a hostile takeover, and the subject will be savaged; access to the subject and sources has been limited because the biographer has gone negative; it is best to wait for the full life — presumably the one the authorized biographer publishes.

Put aside the possibility that the authorized biographer operates under limitations as well — such as the psychological and perhaps even legal burden of being beholden to the subject or the subject’s estate — and consider that quite a different set of problems confront certain unauthorized biographers.

Without the imprimatur of the subject and her intimates, the unauthorized biographer can become overly cautious, bending too far in the direction of bland fairness, lest reviewers deem the biography mean. This is not a hypothetical concern: One reviewer of my Norman Mailer biography actually asserted it was too fair to be really interesting. The comment itself may not have been fair, but it is indicative of the restraints that unauthorized biographers suffer. The editor of the Susan Sontag biography my wife and I wrote favored an “on the one hand this, on the other hand that” approach to forestall the fear that another editor expressed: By taking a sharply critical perspective on our subject we would be leading with our chins.

So my antenna went up when Alice Sparberg Alexiou mildly noted that Jane Jacobs would have nothing to do with “Jane Jacobs: Urban Visionary.” The result is a well-intentioned, informative, but tepid biography. Ms. Alexiou is a great admirer of Jacobs — no problem there since there is plenty to admire — but Jacobs was a firebrand (she died April 25, 2006), and her biographer ought to be as fiercely inquisitive as her subject was. Although Jacobs’s obstreperous behavior goes back as far as challenging teachers in grade school, the biographer does not really grapple with the consequences of being someone as assertive as Jane Jacobs.

Jacobs attended college for only two years and had no formal training as an architect or city planner. She married an architect, though, and wrote for architectural magazines with a fresh vision that could not be learned in any academy. Her signal achievement, “The Death and Life of Great American Cities”(1961), turned city planning on its head.

This was the age of “urban renewal,” by which city planners meant slum clearance and the building of high-rise, low-cost housing for the urban poor while at the same constructing civic showcases like Lincoln Center. Jacobs opposed this thinking — she believed the Robert Moses school of urban design effectively destroyed neighborhoods and a sense of community, actually contributing to urban congestion by inviting the automobile into places like Washington Square via massive highways. When the park was closed off to traffic, both business and the community profited because urban congestion decreased.

Jacobs lost more battles to Moses and his ilk than she won. And would we really want to do without Lincoln Center? As Ms. Alexiou notes (repeating what other critics have said), Jacobs was better at pointing out the negatives of urban renewal than she was at prescribing remedies. Not everyone could live in the messy funk of Greenwich Village and love it as Jacobs did.

Certainly suburban sprawl — the bête noire of Jane Jacobs — can be ugly and wasteful, but the suburbs themselves are surely not the problem. And this is where Ms. Alexiou’s failure to confront Jacobs’s rather crabbed personality is telling. Ms. Alexiou affirms that Jacobs loved the city “passionately and unconditionally.” Not a good thing for a critic, I would say.

When families began to flee the cities after World War II, it was not just a matter of white flight and escaping high crime rates, or a bad case of indulging in conspicuous consumption. This movement embodied a desire for space and a modicum of privacy. Not everyone wants to sit on those stoops Jacobs extolled. When my family moved into the suburbs from Detroit, I watched my grandmother take immense pleasure in creating a garden — her own bit of land, something she had not had since leaving her life as a peasant in Poland in 1911. I went to a new high school and marveled at how the doors to the classrooms had different colors, and how the one-story school had a human scale lacking in Pershing High School, the rather grim edifice I dreaded when I walked toward it on the east side of the city.

What kind of woman could see beauty only in a city or presume that those raucous urban neighborhoods were some kind of ideal form of living? To this question Ms. Alexiou has no answer. I wanted to know more about the Jacobs who did not live only in her books. Here, for example, is just about all the biographer has to say about Jacobs’s wedding: It took place in Jacobs’s hometown, Scranton, Pa. It was a modest ceremony. “Miss Butzner [Jacobs’s maiden name] will wear a white, streetlength dress trimmed with turquoise and fuschia, and a corsage of white orchids.”This and a few other quotations come from the local newspaper. What I want to know is did Jacobs wear this getup, or did she, at the last minute, decide the corsage was too much?

My complaint may seem trivial, but it is indicative of a larger problem: How did Jacobs actually behave and what was this event and others actually like for her? About her attraction to Robert Hyde Jacobs, she is quoted as saying: “Cupid really shot that arrow.” I realize Jacobs resisted the biographer’s prying into her life. But that does not let the biographer off.

Jacobs deserves her historic place for shaking up conventional thinking about urban design. This is why a much tougher, inquiring Robert Caro-style biography, is required.

crollyson@nysun.com