Propositional Imagination and Justification of Modal Beliefs

In this paper I evaluate Geirsson’s justification model for modal beliefs which he proposes in “Conceivability and Defeasible Modal Justification” (2005). Geirsson’s justification model is based on conceivability. Geirsson gives an analysis of conceivability in terms of imagination. Geirsson admits that his account is similar to Yablo’s model, but he claims that it advances discussion in several ways. One of the claimed improvements is to employ propositional imagination for justification of modal beliefs. In this paper I will argue that Geirsson’ claimed advancements are not very useful. For among other things propositional imagination as he defines it could not provide justification for modal beliefs. Moreover Geirsson could not give an answer to the question “what exactly is propositional imagination?” based on which what he considers propositionally imaginable, e.g. denial of Goldbach's conjecture, would still be imaginable but metaphysically impossible propositions would not be propositionally imaginable.