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 Cerdá, 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

• The science of urban design?