 Both Stephen Yablo (1993) and David Chalmers (1996, 2002, 2004, 2010: Ch. 6) have developed independent accounts of conceivability as a source of modal knowledge (for yet another account based on response-dependence, see Menzies 1998). Yablo holds that, when adequately understood, conceivability provides defeasible evidence for possibility. In Yablo’s account, the relevant notion of conceivability involves the imaginability of a situation in which a conceived proposition is taken to be true by the subject in question. Yablo offers the following two conditionals for describing the appropriate philosophical notion of conceivability which provides evidence of possibility (1993: 29)