 The fact is, according to Shepherd, most people believe that their sensations have continued existence, even though they readily allow that pleasures, pains, and various other sensations cease to  exist when they disappear from consciousness (EASP: 9). She denies that sensations that exist unperceived can be understood. It is rather imagination that associates sensations with ideas that represent objects perceived by sense as existing unperceived. The mind has no resources for thinking of such objects except under the form of their sensory appearances. Although the error in supposing sensations exist unperceived can be exposed, this hardly prevents our frequently falling into it. Yet this is not entirely unfortunate, as Shepherd sees it, because it is the means by which we acquire structural as well as existential knowledge of the external world (see  § 5.2).  