  Central to Vaihinger’s project in the PAO is a distinction between two sorts of fictions: (1) what he (somewhat inaptly) terms ‘semi-fictions,’ which are “methods and concepts based upon a simple deviation from reality” (PAO 59); and (2) ‘real’ or ‘genuine fictions’ which are self-contradictory concepts (ibid.).  In other words, semi-fictions are statements or propositions that happen not to correspond to the world; genuine fictions are those that claim something impossible about the world.