The case is made that architectural design needs to be organized hierarchically. A method and formula for doing so are derived based on biology and computer science. Fractal simplicity, in which there is self-similar scaling, replaces the outdated notion of rectangular simplicity. Architectural units on different scales are able to cooperate in an intrinsic manner to achieve an emergent property, which is not present in the individual components. The theory of hierarchical systems from Engineering Science explains how to relate different scales to each other. In buildings, the correlation between architectural scales determines whether a structure is perceived as coherent or incoherent, independently of its actual design, form, and composition. This Chapter presents a scientific proof of why organized detail (i.e. small-scale ornament) is essential to the overall coherence of architectural forms.