  Perceptual beliefs, like the belief that ‘there is a horse over there’, will be explained, in Epicurus' theory, in terms of sense-impressions and the application of concepts (‘preconceptions’; for discussion cf.  Asmis 1999, 276-83), and concept-formation is in turn explained in terms of sense-impression and memory. According to Diogenes Laertius' summary (L&amp;S 17E1-2), the Epicureans say that 