Derek Parfit

Reasons and Persons, published in 1984, reshaped debates about personal identity, rational choice, and ethics. Its thought experiments about teleportation, future selves, and population ethics remain widely discussed.

Parfit argued that personal identity may matter less than psychological continuity and connectedness. In Reasons and Persons, he uses cases such as teletransportation to challenge the idea of a simple, permanent self.

The Repugnant Conclusion is a problem in population ethics associated with Parfit's work. It asks whether a very large population with lives barely worth living could be judged better than a smaller population with much higher welfare.

On What Matters is Parfit's later multi-volume work on moral philosophy, first published in the 2010s. It argues that major traditions such as Kantian ethics, contractualism, and consequentialism may converge more than philosophers often assume.