My thesis project, Letter Spirit, models central aspects of human creativity on a computer with a focus on perception. Letter Spirit explores the creative act of artistic letter-design. The aim is to model how the 26 lowercase letters of the roman alphabet can be rendered in many different but internally coherent styles. Letter Spirit addresses two important aspects of letterforms: the conceptual sameness possessed by letters belonging to a given category (e.g., `a') and the stylistic sameness possessed by letters belonging to a given style (e.g., Helvetica). The program will start with one or more seed letters representing a style, and create the rest of the letters in such a way that all 26 share the same style, or spirit.