The basic premise, in my own words, is that healthy cities exhibit emergent order, a vitality that cannot be reduced to its constituent parts and copied for use elsewhere or scaled up.
She writes that the conditions for a healthy urban area are density, a diversity of uses, a diversity of buildings, and human scale.
The classic example from the book of one of the emergent properties of a health neighborhood is that it allows for many “eyes on the street,” meaning residents, business proprietors, etc., all self-policing the street and subtly interacting in a way to provide safety.
A point I haven't seen referenced as much else where is that Jacobs believed that older buildings were needed in every neighborhood in order to provide lower rents for smaller businesses. I.e., to allow for the survival of mom and pop places that can’t afford the amenities that come with new buildings.
While Jacobs is known as the great rival to Robert Moses, who sought to impose big plans on cities and clear the way for cars, she doesn’t dedicate too much space to him or his ideas in this book (except to discuss at length the trade-off between car-friendly and human-friendly places).
Instead, her bigger intellectual foil is Le Corbusier and his idea of the “Radiant City” -- the ultimate top-down, abstracted, centralized approach to city planning.
In the last chapter, she warns against viewing a city as a work of art (as Le Corbusier did) or thinking of urban planning as a science.
Instead, she recommends:
- Thinking about cities in terms of processes. That is, considering the interactions between people that shape a space for commerce, residence, leisure, etc.
- Relying on induction rather than generalization.
- Learning about the average from the exceptional cases.
Jacobs was writing in 1961. At that point, some of the major problems in U.S. urban planning were already apparent, but just in their very early stages.
Jacobs was aware of some of the malign incentives created by the system of housing finance. And she expected those problems to persist, including as manifested in urban sprawl. Yet I don’t think she anticipated, in this book (she died in 2006), just how much sprawl would reshape U.S. metropolises. The book is about issues in urban neighborhoods, less so about cities as a whole.
One prescient passage, though, notes that the favorable financing for surburbia was not purely a market phenomenon, but rather an outcome desired by “high-minded social thinkers.” She notes that Herbert Hoover opened the first White House Conference on Housing, in 1931, with a “polemic against the moral inferiority of cities and a panegyric on the moral virtues of simple cottages, small towns, and grass.”
Density is a major advantage for neighborhoods, in Jacobs’ view. She notes that, at that time, people confused high density and overcrowding. Her model neighborhood is Boston’s North End. The North End is one of the very few American neighborhoods that is almost medieval in the density of its physical layout.
Confusion about density vs. overcrowding, which probably still persists today, is one of the factors that led authorities to entertain the idea of slum clearance.
Jacobs, on the other hand, counted on organic processes to “unslum” bad neighborhoods. No need to push people out and radically rebuild.
Sadly, she was mistaken about the prospects for poor African-American urban neighborhoods. She thought they would be gradually improved and “unslummed” the way other neighborhoods were. If she was aware of the possibility of what we would now call gentrification, it’s not reflected in the book.