This paper examines the role of certain graphic metaphors as generators of form in computer aided design. An introduction establishes that representation in architectural design is largely metaphorical, that metaphor is only one among several types of rhetorical turns, and that such turns can be of value in the design process. The paper then describes a case study a residential design project in which the author used a 3D computer-based modelling program to produce a type of strained rhetorical turn called catachresis. Through a series of catachrestic moves, conventional representations were made to yield unconventional architectural meanings. Next the paper discusses inferences from the case study regarding the play of rhetorical turns in computer aided design. The paper concludes with suggestions for catachrestic “wild cardi and indeterminate functions in CAD systems to keep design processes and products open to uncertainty.