In this thesis I will test Yagisawa´s Extended Modal Theory of modality against two issues: the problem of accidental intrinsic properties and the problem of transworld identification. Both are part of the recurring criticism of theories supporting transworld individuals, such as the Extended Modal Theory. The first is based on Lewis criticism that argues that if a theory claims that individuals exist in more than one possible world, then transworld individuals do not possess intrinsic properties, only external ones. The second follows the rational of Quine, that argues that because anything can become anything by follow a chain of possible worlds, it becomes problematic in some cases to “discover” the modal stage of a transworld individual in another possible world. The discussion concludes that despite of the criticism above, Yagisawa provides convincing arguments to support transworld identity and EMR does a better job than the Counterpart theory in explaning modality.