From Cross-World Predication to Cross-World Travel:
Building a Bridge between Worlds
Brandon Ryan Hoogstra

Abstract:
Within his book On the Plurality of Worlds, David Kellogg Lewis provides an extensive elucidation of his theory of modal realism, which states that all possible worlds are concrete particulars with ontological status equal to that of the actual world. The general conceptualization of modal realism advocated for by Lewis is highly beneficial for the purposes of comprehending such notions as cross-world predication, cross-world interaction, and cross-world travel. Cross-world predication is the process of identifying a relation between entities contained within distinct possible worlds. For example, the proposition ‘I could have been wealthier than I actually am’ involves predicating between the inhabitants of distinct possible worlds, as the actual individual referenced within such a proposition and his or her wealthier counterpart reside within different worlds. Properly understanding the proposition ‘I could have been wealthier than I actually am’ requires imagining a counterfactual scenario in which the closest counterpart to the referent of the term ‘I’ possesses a higher caliber of wealth than the individual who is instantiating the proposition. Expanding upon the theme of cross-world behaviors, cross-world interaction occurs when the events that transpire within one possible world causally impact the events that transpire within another possible world. Furthermore, cross-world travel occurs when an entity that is contained within one possible world departs from said world and arrives within another possible world. Although Lewis himself explicitly denies the potential for both cross-world interaction and cross-world travel, it is possible to account for such ideas with a few relatively minor modifications to his theory of modal realism. The primary hypothesis of the present research initiative may be tersely summarized as the theory that a formal language with an expressive power sufficient to adequately represent propositions involving cross-world predication is simultaneously capable of representing both propositions involving cross-world interaction and propositions involving cross-world travel. An alternative way of understanding the preceding idea is that when a formal language is able to satisfactorily account for the notion of cross-world predication, the distinct notions of cross-world interaction and cross-world travel can be had “for free”, without any features or qualities being added to the language. The first main objective of the present research initiative is to demonstrate that a formal language that is capable of representing cross-world predication is able to represent the distinct notions of cross-world interaction and cross-world travel as well. The second main objective of the present research initiative is to provide a description of the logical coherency of such notions as cross-world interaction and cross-world travel, as well as their usefulness for philosophical theorizing, particularly within the context of an appropriately-modified form of the Lewisian theory of modal realism. Finally, the present research initiative illustrates its significant philosophical utility through the practical application of a case study of the sophisticated system of modal metaphysics of the DC Extended Universe.