The “duplication problem” for psychological theories of personal identity over time

Question 1

The duplication problem

Answer 1

Suppose someone invents teletransportation and it works as follows:
- A person enters the machine and it scans their body, recording all of their body’s + brain’s information
- Their body is destroyed
- In that instant, their body’s and brain’s information is radioed to another location, where local matter is combined and arranged as per the information
- The result is a person with a fully functioning human body + brain that is a replica of the one that entered the machine and with the same beliefs/desires/character traits/memories, etc

Question 2

Thoughts on the duplication problem

Answer 2

• Body theorists refuse this view that the replica person is numerically identical with the person who entered the transporter
• This is because the transporter destroys the bodies of the people who step into it.
• However, psychological continuity theorists accept this view

Question 3

Contradiction to the theory

Answer 3

• There is a malfunction, and two copies of you are created, both of which are associated with persons who appear to be psychologically continuous with you before entering the machine
  ○ A= you at T1
  ○ B and C at T2
  So, who is “you” at T2?

Question 4

Optional solutions

Answer 4

1. You are B but not C. Problem; arbitrary
2. You are C but not B. Problem; arbitrary
3. You are B and you are C. Problem; seems to violate the transitivity of identity
4. You are neither B nor C, you have ceased to exist. Problem; How could a double success be a failure?
5. B and C form a “composite person” P and you are P. Problem; weird
6. There was never only one you to begin with, there were two people, sharing your brain, body, and course of experience all along, and the operation simply separated them. Problem; there didn’t seem to be more than one person where you were at T2
   *Overall, the question is empty; it has no determinate answer either way.

Question 5

Parfit’s psychological continuity theory (first pass)

Answer 5

• Persons are ongoing streams of psychological continuity
• A person P1 existing at time T1 and a person P2 existing at a later time T2 are the same person if and only if P2 is linked to P1 by a sequence of overlapping chains of strong psychological connectedness

Question 6

Parfit’s psychological continuity theory (second pass)

Answer 6

• Persons are ongoing streams of non-duplicated psychological continuity
• A person P1 existing at time T1 and a person P2 existing at a later time T2 are the same person if and only if P2 at T2 is linked to P1 at T1 by a sequence of overlapping chains of strong psychological connectedness and there is no other person in existence at T2 who is also psychologically continuous with P1 and T1 but not via the sequence linking P2 and P1
• In short: personal identity over time is psychological continuity in the absence of competitors

Question 7

Parfit adds to the revised psychological continuity theory idea that we should respond to the duplication problem in a slightly different way

Answer 7

He believes that personal identity isn’t what we really care about. What truly matters to us is that someone in the future be psychologically continuous with us, not that they’re strictly identical with us. The reason that we think we care about identity is that under normal circumstances, with currently existing technology, securing future identity is the only way to secure future psychological continuity.

Question 8

Consequences to the revised psychological continuity theory

Answer 8

1. Suppose you use the teletransporter and a replica is made of you, as in Parfit’s “branch-line case.” You then find out that in thirty years you will be dead but your replica will still be alive.
   - Parfit’s view entails that you should be willing to pay about as much to prevent your replica from being tortured in the future as you would be to prevent yourself from being tortured in the future.
2. A variation of the branch-line case in which you do not die. Instead as the years go by you change psychologically in drastic ways. So, 50 years from now, you will be psychologically harshly different from you now. but, your replica doesn’t change so much and remains the way you are today. Thus, your future self will psychologically resemble you in a minimal way while your replica with be psychologically continuous with you today.
   - Parfit’s view arguably entails that if you today have a large fortune to leave either your future self or to your replica, you should leave it to your replica.