The acute experimentalism of Finnegans Wake has always created a great deal of uncertainty and even controversy about its fictional, generic, and semantic operation. Is it a representation of a dream, a night world, or some other plane of unreality, or does it offer a narrative, either a relatively realistic one or a version of biblical or mythic or other collective stories? How can one adjudicate questions like this—on the basis of what sort of evidence? This article tackles the problem of how one might sort out the nature of the fictional world or worlds conveyed by the text’s complicated language by turning to a development in the field of narratology called “Possible Worlds“ theory. The theories of Marie-Laure Ryan, among others, offer us tools and criteria for understanding how readers achieve access to fictional worlds like the ones found in Book I, Chapter 1 of Finnegans Wake.