Interior designers have tended, like architects, to determine three-dimensional space using geometry by manipulating representations of material substances or building work. Geometry without substance is of thought only and only has one quantity; number. As such design becomes the manipulation of representations with the traditions of geometry. One of those traditions is the understanding of geometry as pure static Cartesian abstraction impurely expressed in substance. Design has tended to do this for a number of reasons, one of which is to engage more fully with the design of built form and another is to distance itself from decoration. This paper explores the issue and asks three questions: Is the repetition of Enlightenment geometry a necessary condition for architecture and design? If it is, does material substance become merely an excessive characteristic of pure concepts conceived as pure abstract geometry? Is culture becoming so dependent on geometry that to make geometry a pure abstraction is to understand material substance as excessive? These questions are reformulated through the investigative process of the paper and are asked in a different form as a conclusion.