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Exploring what makes a person the same individual over time despite physical and mental changes.
If every cell in your body is replaced every seven years, and every memory you have could be uploaded to a computer, would 'you' still exist, or would you just be a high-quality copy?
The Ship of Theseus is a classic thought experiment: If a ship's wooden planks are replaced one by one until no original parts remain, is it still the same ship? This poses a massive problem for human identity. Biologically, your cells are in a constant state of flux. Most of your cells are replaced within a decade. If identity is based on Physicalism (the idea that you are your body), then you are literally not the same person you were ten years ago. Philosophers distinguish between qualitative identity (looking exactly the same) and numerical identity (being the one and only 'you'). If we define a person at time and , the physicalist must explain what link remains if the matter is entirely different.
Quick Check
If a person undergoes a full-body transplant, does the 'identity' follow the old body or the new parts?
Answer
It depends on your theory: a physicalist might say the identity is lost or changed, while a psychological theorist would look for where the mind went.
John Locke rejected the idea that identity is found in the 'substance' of the body. Instead, he proposed the Memory Theory. Locke argued that consciousness—specifically the ability to repeat in the mind an action past—is what makes a person the same over time. If Person at can remember the thoughts and actions of Person at , then and are the same person. Locke used the 'Prince and the Cobbler' example: if a Prince's soul (and memories) entered a Cobbler's body, the resulting person would be the Prince, despite the physical change. Identity, for Locke, is a chain of psychological continuity.
Thomas Reid challenged Locke with this scenario: 1. A boy is flogged at school (). 2. Later, as a young officer, he takes a standard () and remembers the flogging (). 3. As an old general (), he remembers taking the standard (), but has forgotten the flogging (). By Locke's logic, is , and is , but is NOT . This violates the transitive property of identity: if and , then .
Quick Check
According to Locke, if you completely forget your 3rd birthday, are you the same person who experienced that birthday?
Answer
No; for Locke, the 'self' only extends as far as your current consciousness can reach back into the past.
Derek Parfit took a radical step further, influenced by the Bundle Theory (often associated with David Hume). Parfit argued that there is no 'ego' or 'self' at the center of our experiences. Instead, we are a 'bundle' of mental states—beliefs, memories, and desires—that are loosely connected. Parfit suggests that Identity doesn't actually matter. What matters is Survival through psychological connectedness. He uses the 'Teletransporter' thought experiment to show that if you were destroyed and perfectly recreated on Mars, the 'you' on Mars is just as good as the 'you' on Earth, even if numerical identity is broken. We are like a rope: no single fiber runs the entire length, but the overlapping fibers create a continuous whole.
Imagine a machine that scans your atoms, destroys your body, and beams the data to Mars to be reconstructed. 1. Scenario A: The machine works perfectly. Is the person on Mars 'you'? 2. Scenario B: The machine scans you but fails to destroy your original body on Earth. Now there are two 'yous' with the same memories. Parfit argues that since identity must be 1-to-1, but 'survival' can be 1-to-many, the concept of a 'single identity' is a linguistic mistake. You 'survive' in both, but you are 'identical' to neither.
Which philosopher would argue that you are the same person as your 5-year-old self ONLY if you can remember being that child?
What does the 'Brave Officer' paradox primarily critique?
Derek Parfit believes that being 'numerically identical' is the most important part of being a person.
Review Tomorrow
In 24 hours, try to explain the 'Prince and the Cobbler' story to someone else and why it supports Locke's view.
Practice Activity
Journaling Exercise: Write down three memories that define 'you.' If you lost those three memories tomorrow, would you still be the same person? Why or why not?