 All of these uses illustrate the general notion of ‘part’ that forms the focus of mereology, regardless of any internal distinctions. (For more examples and tentative taxonomies, see Winston et al. 1987, Iris et al. 1988, Gerstl and Pribbenow 1995, Pribbenow 2002, Westerhoff 2004, and Simons 2013.) Sometimes, however, the English word is used in a more restricted sense. For instance, it can be used to designate only the cognitively salient relation of parthood illustrated in (1), the relevant notion of salience being determined by Gestalt factors (Rescher and Oppenheim 1955; Bower and Glass 1976; Palmer 1977) or other perceptual and cognitive factors at large (Tversky 2005). Or it may designate only the functional relation reflected in the parts list included in the user's manual of a machine, or of a ready-to-assemble product, as in (2), in which case the parts of an object x are just its “components”, i.e., those parts that are available as individual units regardless of their actual interaction with the other parts of x. (A component is a part of an object, rather than just part of it; see e.g. Tversky 1989, Simons and Dement 1996.) Clearly, the properties of such restricted relations may not coincide with those of parthood understood more broadly, and it will be apparent that pure mereology is only concerned with the latter. 