The growing diffusion of perspectivism within the debate on information system ontologies [ISOs] does not correspond to a thorough analysis of what perspectivism specifically consists of. This paper aims to fill this void. First, I show what supporting perspectivism in information system ontologies [PISO] means in terms of (minimal) claims and implications; then I argue that the definitions of ISO implicitly assume PISO’s (minimal) claims or, in other words, that ISOs presuppose and maintain PISO. Section 2 presents the main definitions (...) of ISO. Section 3 specifies what claims are common to all perspectivists in ISO. Sects. 4–7 analyze the implications of those claims. Section 8 explores the chance of multiple perspectivisms within ISOs’ domain. Finally, Sects. 9–10 assume that, if PISO’s (minimal) claims and (their) implications can be inferred from ISO’s definitions, then ISOs are perspectivist, or PISO’s minimal claims are assumptions underlying ISOs. (shrink)