Extension Through Logical Space
This thesis discusses three different theories of de re modality, i.e., the ways particular individuals could be, or must be. It defends the counterpart theory as the best theory of de re modality for modal realists. In other words, I argue that Ruth is ‘at possible world w’ by having a counterpart that is distinct from and yet suitably similar to our Ruth, at world w. Chapter I will be a brief introduction. In Chapter II, I will define my terms and spell out my assumptions. In Chapter III, I will describe the three theories of de re modality: counterpart theory, trans-world identity theory and trans-world fusion theory. In Chapter IV, I will present a version of counterpart theory based on Lewisian modal metaphysics, provide four independent utility arguments for counterpart theory, and respond to Humphrey’s objection to counterpart theory. In Chapter V, I will present Lewis’s version of trans-world identity theory based on Lewisian modal metaphysics and his objections against such a view. I will explain two alternative versions of trans-world identity theory based on alternative modal metaphysics and then argue against such attempts. In Chapter VI, I will spell out trans-world fusion theory in detail, present an argument from vagueness for trans-world fusion theory and argue against it. In Chapter VII, I will provide a short conclusion.