Personal Identity in Parallel Universes

Imagine you travel to a parallel universe, where you happen to find a planet like the Earth, where you find a city like New York, where you find a university like Columbia University, where you find a person like you. Call that person X. You are staring at X. What is the relation between you and X, the other-worldly you? This is the famous “problem of transworld identity” hotly debated since the 1960s. In this course, we will be reading the two most influential books in contemporary analytic philosophy: Saul Kripke’s Naming and Necessity (1972) and David Lewis’s On the Plurality of Worlds (1986) – where two completely different answers are forcefully argued for. Kripke argues that you and X are one and the same person. (If you kill X, will you die?) Lewis argues that you and X are merely similar strangers. (Not unlike you encounter someone who looks like you in another country.) We will start with Ted Sider’s Four-Dimensionalism (2001) – the most influential book on what turns out to be a closely analogous problem: identity over time. All these will lead up to a completely novel theory: Five-Dimensionalism (5D), which argues that you and X are parts of the same person, like your left hand and right hand are both part of your body. According to 5D, you are five-dimensional, extended across 3D space, time, and possible worlds. You are all the possible yous. There is no prerequisite for this course.