 The conceptualist might hope to avoid these problems, without falling back on Lewis’s concrete realism about possible worlds, by understanding worlds in terms of properties or states of affairs, rather than propositions.  Following Stalnaker (1976), one might think of worlds as properties which are ways things could have been. Following Plantinga (1974) and others, one might think of worlds as maximal consistent states of affairs, where these are thought of as distinct from propositions. 