The Unimportance of Identity

December 8, 2025 | 1,003 words | 5min read

Paper Title: The Unimportance of Identity

Link to Paper: https://philpapers.org/rec/PARTUO

Date: 1997

Paper Type: Philosophy, Ontology, Identity

Short Abstract: In this paper Derek Parfit argues that identity itself is not an interesting concept to study. Instead, we should focus on the underlying physical and psychological facts.

0. Basic Premise and Question

Imagine that far in the future we invent a teletransporter: a machine which, when I press a button, destroys my body through atomization, records the exact state of all my cells, and sends this information to Mars, where my body is reconstructed atom by atom.

The person who wakes up on Mars remembers my life up to the moment I pressed the button and, in every other way, seems exactly like me.

The question is: is that person me or not? Some believe it is me; others believe the person who wakes up is merely a replica.

1. The Unimportance of Identity

We can distinguish two questions of identity:

• Qualitative identity: two objects have the same properties.
• Numerical identity: two objects are literally one and the same object.

For Parfit, the second question—numerical identity in relation to persons, is the central one.

Leibniz, with his principle of the indiscernibility of identicals, concluded that numerical identity implies qualitative identity. But the reverse may not be true.

Thus the question becomes: When are two persons the same? Is the person we spoke to yesterday or a week ago literally the same as the one today?

There are various criteria for identity:

Bodily continuity

Person X at time t1 is identical to person Y at time t2 if X has the same body at both times.

• In the teletransporter case, we do not have bodily continuity, so this view says the person on Mars is not me.
• Counterexample: brain transplantation. If our brain is transplanted, we normally would still consider ourselves to survive.

Psychological continuity

Person X at t1 is identical to person Y at t2 if X and Y share psychological continuity (memory, attitudes, convictions, preferences, etc.)

• Under this view, the person in the teletransporter is me.
• Counterexample: duplication. If we perfectly clone you, who are you then? Are you suddenly two persons? Most people would say “no,” which suggests psychological continuity alone cannot define identity.

Cartesian egos (dualism)

There is a second, non-physical substance that makes us who we are.

• Counter: almost nobody today accepts dualism due to the interaction problem and other well-known objections.

Redcutionism

Another way to examine identity is reductionism, which comes in different versions:

• Identifying reductionism: persons are just bodies.
• Constitutive reductionism: a person is an entity that has a body, thoughts, and experiences.
• Eliminative reductionism: there is no such thing as “the person”—only brains, bodies, thoughts, and experiences.

Parfit adopts a reductionist view. Just as calling a group of trees a “copse” adds nothing beyond the facts about the trees, Parfit claims that facts about persons are nothing over and above facts about bodies, brains, psychological continuity, and connectedness. The concept of identity does not add new information.

Parfit offers several thought experiments:

• Different percentages of your cells are replaced, from 0% (clearly still you) to 100% (clearly a replica).
• In the middle cases (30%, 50%, 70%), there is no clear answer.

For identity to always be yes/no, there would have to be a precise cutoff—one more replaced cell suddenly makes you “not you.” This seems absurd. No one could ever discover such a cutoff, and the resulting person would always believe themselves to be you.

We can always ask, “Would that future person be me?” But in many cases, the question has no answer—it becomes empty. This is similar to asking: how much territory or how many people can we remove before a nation stops being that nation? We accept that such a question is empty in the case of nations, but not in the case of identity.

But then a deeper question appears: How can it be neither true nor false that I exist tomorrow?

Reductionism offers the answer: there is only the actual course of events—a certain physical and psychological continuity. The question “Is the future person me?” is really a question about how to describe that course of events, not a question about additional facts.

Once all physical and psychological facts are known, questions about identity become merely linguistic. Reality does not change depending on whether we apply the label “same person.”

When we are at a university, the interesting questions are not “Is this still a university?” or “How many chairs can we replace before it stops being one?” The interesting questions concern how the university functions.

Similarly, for legal or practical purposes we might need to answer identity questions, but these answers do not solve any deeper metaphysical issue—they are merely decisions.

2. What Actually Matters

Identity is not a deep fact about the world. Once we know all physical and psychological facts, identity adds nothing further—just as calling a group of trees a “forest” adds nothing if we already know everything about the trees and their relations.

People think they care about identity because they care about the future self. But they do not care about identity as such—they care about whether the future person is psychologically continuous with them.

Consider a head transplant: identity plays no essential role in deciding whether the operation is good or bad. The resulting person has your head, brain, psychology, and memories. His life continues your projects and thoughts. Whether he is “you” is only a verbal question.

Some questions genuinely ask about reality:

• Will I feel pain during the surgery?

Some questions ask only about words:

• Does seasickness count as “pain”?

In the head-transplant case, we know exactly what will happen physically and psychologically. The question “Will the resulting person be me?” is like the seasickness case: a question about words, not facts.

Similarly, if 20%, 50%, or 70% of your cells are replaced, we already know exactly what will happen physically and psychologically. The remaining uncertainty is only about how to describe it.

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