 Wolff’s analysis of physical bodies is given from two different perspectives. First is the “bottom-up” metaphysical account of bodies, where bodies are defined as aggregates of simple substances, and second is the “top-down” mechanistic description, where the reality of bodies, given by the testimony of the senses, is explained in terms of interacting primitive corpusula (or corpuscles). To facilitate our discussion, we should identify the three levels of description that Wolff employs when giving his two perspective account. Identifying these three different levels is helpful in understanding at what respective point the mechanical and metaphysical accounts each terminate or bottom out.