The underlying idea is that of moving away from the typically American notion of dense urbanism, in the form of a high-rise downtown, as the exclusive realm of business and commerce, and instead considering ways to construct a dense urban environment that is appealing as a place to live, rather than simply to work or to shop. The late 19th and early 20th century American city, as impressive as its downtown appears to us in old drawings and photos today, utterly failed at this task for the most part. In spite of notable successes in New York and Boston, cities which had traditions of dense residential living predating the industrial revolution, most places failed to offer a compelling vision for apartment or very high-density single family living to middle class families.
The principles the authors set out thirty years ago lay the foundation for thinking about what conditions are required for a sound urban environment:
"There are five physical characteristics that must be present if there is to be a positive response to the goals and values we believe are central to urban life. ... All five must be present, not just one or two. There are other physical characteristics that are important, but these five are essential: livable streets and neighborhoods; some minimum density of residential development as well as land use; an integration of activities -- living, working, shopping -- in some reasonable proximity to each other; a manmade environment that defines public space (as opposed to buildings that, for the most part, sit in space); and many, many separate buildings with complex arrangements and relationships."Still, the authors warn, "the quest for livability, if pursued obsessively, can destroy the urban qualities we seek to achieve." Excessive street width in the name of safety and sunlight; excessive green space in the name of health and recreation; excessive setbacks for noise and privacy; all these, the authors note, can undermine the density and enclosure essential to maintaining an environment that is both dense and appealing. A minimum density, the authors surmised, was 15 units per acre, a figure squarely in the middle of the range Jane Jacobs derisively termed a "semisuburb," (Death and Life, p. 273), though in the prologue Jacobs suggests that that figure ought to have been set higher.
These points may seem obvious or elementary from today's standpoint, but the observation that cities fundamentally must work to provide an appealing environment for residential living remains a primary challenge for American cities today.