The Four Conditions of Vitality

In The Death and Life of Great American Cities, Jacobs identified four conditions that must be present for urban diversity to emerge. They are not prescriptions derived from theory; they are patterns she observed across cities that generated diversity and cities that did not. She argued that all four must be present simultaneously; absence of any one is sufficient to suppress vitality regardless of the others. The four conditions are: mixed primary uses (the neighborhood must serve more than one primary function); short blocks (creating more intersections and more opportunities for chance encounter); buildings of varying age (including cheap old buildings that can host experimentation); and sufficient density of people (enough to support the diverse enterprises that diversity requires).