Abstract: While there is broad consensus on the roles propositions can play (they are the bearers
of truth values, meanings of sentences, and/or objects of beliefs and attitudes), there is
far less consensus on their metaphysical nature. Some philosophers claims that
propositions are sets of possible worlds. This thesis examines this claim with a
particular focus on modal realism, the idea that these possible worlds are concrete
entities of the same sort as the actual world. I examine two problems: first I determine
whether sets of Lewisian worlds are the kind of objects we have epistemic access to,
and if this alters their ability to take the propositional role. I then compare Lewisian
propositions to their structured counterparts to determine if any other theories are
more accurate at modeling content. I conclude that the structured propositional view of
Jeffrey King solves many of the issue Lewisian propositions encounter while being
conservative enough for a modal realist to adopt it with minimal sacrifices.
