Compared with the Physical Criterion, the Narrow Psychological Criterion adds the requirement of psy… — Derek Parfit

Compared with the Physical Criterion, the Narrow Psychological Criterion adds the requirement of psychological continuity with its normal cause to mere brain survival, while the Wide Psychological Criteria allow teletransportation-style cases—where a new but psychologically continuous brain is produced by a reliable non‑normal process—to count as survival; Parfit suggests that we may not need to decide definitively between these versions.

By Derek Parfit, from Les raisons et les personnes

Key Arguments

He restates the Physical Criterion: 'On the Physical Criterion, a person continues to exist if and only if (a) there continues to exist enough of this person’s brain so that it remains the brain of a living person, and (b) there has been no branching in this physical continuity, (a) and (b) are claimed to be the necessary and sufficient conditions for this person’s identity, or continued existence, over time.'
He then formulates the Narrow Psychological Criterion as adding psychological requirements: 'On the Narrow Psychological Criterion, (a) is necessary, but not sufficient. A person continues to exist if and only if (c) there is psychological continuity, (d) this continuity has its normal cause, and (e) it has not taken a branching form, (a) is required as part of the normal cause of psychological continuity.'
In his teletransportation scenario, the Scanner destroys his brain and body and produces 'a person who has a new but exactly similar brain and body, and who is psychologically continuous with me as I was when I pressed the green button. The cause of this continuity is, though unusual, reliable.'
He notes that 'On both the Physical Criterion and the Narrow Psychological Criterion, my Replica would not be me. On the two Wide Criteria, he would be me.', highlighting how the choice between Narrow and Wide versions affects our judgment about such cases.
He introduces a 'partial analogy' to suggest that it may be unnecessary to decide between these versions, foreshadowing the artificial‑eye example: 'I shall argue that we need not decide between these three versions of the Psychological Criterion. A partial analogy may suggest why.'

Source Quotes

The continued existence of a person’s brain is at least part of the normal cause of psychological continuity. On the Physical Criterion, a person continues to exist if and only if (a) there continues to exist enough of this person’s brain so that it remains the brain of a living person, and (b) there has been no branching in this physical continuity, (a) and (b) are claimed to be the necessary and sufficient conditions for this person’s identity, or continued existence, over time. On the Narrow Psychological Criterion, (a) is necessary, but not sufficient.

On the Physical Criterion, a person continues to exist if and only if (a) there continues to exist enough of this person’s brain so that it remains the brain of a living person, and (b) there has been no branching in this physical continuity, (a) and (b) are claimed to be the necessary and sufficient conditions for this person’s identity, or continued existence, over time. On the Narrow Psychological Criterion, (a) is necessary, but not sufficient. A person continues to exist if and only if (c) there is psychological continuity, (d) this continuity has its normal cause, and (e) it has not taken a branching form, (a) is required as part of the normal cause of psychological continuity.

On the Narrow Psychological Criterion, (a) is necessary, but not sufficient. A person continues to exist if and only if (c) there is psychological continuity, (d) this continuity has its normal cause, and (e) it has not taken a branching form, (a) is required as part of the normal cause of psychological continuity. Reconsider the start of my imagined story, where my brain and body are destroyed.

Reconsider the start of my imagined story, where my brain and body are destroyed. The Scanner and the Replicator produce a person who has a new but exactly similar brain and body, and who is psychologically continuous with me as I was when I pressed the green button. The cause of this continuity is, though unusual, reliable. On both the Physical Criterion and the Narrow Psychological Criterion, my Replica would not be me.

The cause of this continuity is, though unusual, reliable. On both the Physical Criterion and the Narrow Psychological Criterion, my Replica would not be me. On the two Wide Criteria, he would be me. I shall argue that we need not decide between these three versions of the Psychological Criterion.

On the two Wide Criteria, he would be me. I shall argue that we need not decide between these three versions of the Psychological Criterion. A partial analogy may suggest why. Some people go blind because of damage to their eyes.

Key Concepts

On the Physical Criterion, a person continues to exist if and only if (a) there continues to exist enough of this person’s brain so that it remains the brain of a living person, and (b) there has been no branching in this physical continuity, (a) and (b) are claimed to be the necessary and sufficient conditions for this person’s identity, or continued existence, over time.
On the Narrow Psychological Criterion, (a) is necessary, but not sufficient.
A person continues to exist if and only if (c) there is psychological continuity, (d) this continuity has its normal cause, and (e) it has not taken a branching form, (a) is required as part of the normal cause of psychological continuity.
The Scanner and the Replicator produce a person who has a new but exactly similar brain and body, and who is psychologically continuous with me as I was when I pressed the green button. The cause of this continuity is, though unusual, reliable.
On both the Physical Criterion and the Narrow Psychological Criterion, my Replica would not be me. On the two Wide Criteria, he would be me.
I shall argue that we need not decide between these three versions of the Psychological Criterion. A partial analogy may suggest why.

Context

Same later part of Section 78, where Parfit directly compares the Physical and Narrow Psychological Criteria and explains how Wide Psychological Criteria treat teletransportation differently, before introducing an analogy to motivate agnosticism between them.