Some mechanists reserve the term “mechanical models” for models that describe the entities, activities, and organizational features of a system. According to Glennan’s (2005) account, a mechanical model that leaves out some relevant features is, ipso facto, incomplete and sketchy. One specific instantiation of this debate concerns the explanatory force of functional models in psychology. Piccinini and Craver (2011) argue that such models should be understood as mechanistic sketches, black-box models to be evaluated and filled in as details about the underlying mechanism are discovered. Black box models are incomplete in virtue of leaving out details about underling mechanisms and that those models ultimately depend for their explanatory force on the promise that the functional models do, in fact, correspond to how the mechanism works. (See Weiskopf 2011 for a criticism of this account and Povich forthcoming for a response) 