Lesson · 4 min Stretch
The Teleporter
In one line Parfit argued that personal identity is not what matters; what matters is the continuity of memory, character and plans.
Derek Parfit, in Reasons and Persons from 1984, asked you to imagine a teleporter. It scans your body on Earth, destroys it, and builds an exact copy on Mars, with your memories, character and plans. Is the person on Mars you, or a new person who only thinks so?
Now suppose the machine fails to destroy the original, or makes two copies. Both are psychologically continuous with you, but they cannot both be you, since they are two people. Parfit concluded that identity is not what matters in survival. What matters is the chain of psychological connections, and that can hold to two people at once or fade by degrees.
He found this freeing. The wall between himself and others seemed thinner, and he cared less about his own death.
Go deeper
Critics such as Bernard Williams pressed the other side. Imagine being told you will be tortured tomorrow, but first your memories will be erased and replaced. You would still dread the pain, Williams argued, which suggests the body counts for more than Parfit allowed. Animalists such as Eric Olson hold that we are, at bottom, living human animals.
The memory app
An app offers to keep a perfect record of Lena’s messages, photos and habits, and after her death to keep chatting with her family in her voice.
Her family asks whether that would be her. Parfit’s question helps them sort it out: the app copies some links, but not the ongoing life that made new memories, changed its mind and kept its promises. What they care about, they decide, is not a perfect copy but the connections they actually had.
Try this today Picture yourself in twenty years. Ask which links to that person you care about keeping, and why.
Cite or share this lesson
A plain reference you can paste into notes or an essay:
Quest2Reason. “The Teleporter.” https://quest2reason.com/learn/lesson/the-teleporter. Accessed 13 November 2026.
Sources
- Stanford Encyclopedia of Philosophy, “Personal Identity and Ethics” — Covers Parfit’s view that identity is not what matters and its critics.
- Wikipedia, “Teletransportation paradox” — Sets out the teleporter and branching cases.
- Wikipedia, “Reasons and Persons” — Summarizes Parfit’s 1984 book and its argument about personal identity.
- Derek Parfit, Reasons and Persons (1984), Part Three — The teleporter, the branching cases, and the argument that identity is not what matters. Paraphrased; nothing is quoted.