The science of urban design?

In a provocative paper Marshall (2012) suggests that a range of seminal urban design theories stemming from the 1960s - Jacobs, Alexander, Lynch and Cullen - can be construed as pseudo-science because they have not been tested empirically. Adding Sitte and Cerda, we take this provocation as a chance to raise some questions about the nature of urban design knowledge, theory and practice. We suggest that this work is not and cannot be empirical science but is based in the detailed observation of cities using multiple logics. While there is an emerging science of cities, urban design knowledge is much broader, spanning both natural and social sciences as well as the arts and humanities. We also argue that it is a particular form of diagrammatic socio-spatial knowledge that cannot be reduced to either words or numbers. These thinkers remain seminal more for the questions they open than the answers they provide.