Semper's practical aesthetics was meant to provide a vehicle for historical interpretation, a basis for educational reform, and a logical method of inventing. In short, it was to provide a total method for the interpretation, diffusion, and production of architecture and art. So far, I have examined only the first part of this diverse ambition: the comparative method as a vehicle for explaining the historical development of art. Now it is time to approach the final step of the practical aesthetics: the dream of a method to guide not only the interpretation, but also the production of architecture.

Semper's hope of moving from a descriptive to a prescriptive theory of architecture relied on the framework of the comparative method. Although comparative anatomy and linguistics had provided a model for the interpretation of organic wholes, they had been less explicit about the possibility for systematic prediction. The disciplines in which this ambition was formulated most explicitly were neither anatomy nor linguistics, but rather the new sciences of man: sociology and political science. By means of comparison, these disciplines aimed to progress from explanation and description to experimentation and prediction, establishing a science of human culture. This was the ambition that fuelled and informed Semper's method of inventing.