Abstract

Here I first raise an argument purporting to show that Lewis’ Modal Realism ends up being entirely trivial. But although I reject this line, the argument reveals how difficult it is to interpret Lewis’ thesis that possibilia “exist.” Five natural interpretations are considered, yet upon reflection, none appear entirely adequate. On the three different “concretist” interpretations of ‘exist’, Modal Realism looks insufficient for genuine ontological commitment. Whereas, on the “multiverse” interpretation, Modal Realism acknowledges physical possibilities only--and worse, (assuming either axiom S5 or axiom B) each possibilium ends up as a necessary physical existent. Finally, on the “broadly Actualist” of ‘exist’, Modal Realism is either inconsistent or it mistakenly identifies the unrestricted quantifier with the unrestricted Actualist quantifier. The upshot is that it remains obscure in what non-trivial sense Lewisian possibilia “exist.”.