Hybrid theories of diachronic identity

David W. Agler

The Pennsylvania State University

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Hybrid theories

Introduction

  • Soul theory fails
  • Physical theory fails
  • Psychological theory fails

Intuition: Maybe some combination work

General problems

Golden mean reasoning: X is extreme. Y is extreme. Therefore, the mean between X and Y is true.

  • Run 200 miles a week. Extreme
  • Run 0 miles a week. Extreme.
  • Therefore, I better eat run 100 miles a week.

Compromise-style reasoning

When you are little, you are told to compromise.

  • Example: Johnny has all the toys. Johnny should share his toys.

But, sometimes you shouldn’t.

  • Tek: I’ll sell my car to you for 20K (it is worth 21K).
  • Me: How about $1.
  • Tek: No.
  • Me: OK. Let’s compromise. 10K.

Middle-ground truth

A middle-ground position between two false theories does not make the middle-ground theory true.

  • Global warming is increasing temperature by 100 degrees C each year.
  • Global warming is increasing temperature by 50 degrees C each year.
  • Middle ground: Guess it is only increasing by 75 degrees C.

Two problems with hybrid theories

  1. Inherit the problems of the old theories (fixes nothing)
  2. New problems emerge due to hybridizing.

Two kinds

Conjunctive theories

Take two theories and combine them as a conjunction (A and B).

Example: \(A=B\) iff \(B\) at \(t_2\) has the same body and mind as \(A\) at \(t_1\)

Disjunctive theories

Take two theories and combine them as a disjunction (A or B).

Example: \(A=B\) iff \(B\) at \(t_2\) has the same body or the same mind as \(A\) at \(t_1\)

Conjunctive theory problems

  1. Fission: does not solve hemispherectomy transplant (fission) case
  2. Fetus problem: Under the body theory alone, you were a fetus, but the conjunctive theory says you are not.

Disjunctive theory problems

  1. Double fission: hemispherectomy + teletransportation gives you 4 persons.
  2. Brain + psychology swap: Imagine we remove \(A\)’s brain and put it in \(B\)’s body, and then we swap the psychologies of \(A\) and \(B\) post operation.
    • \(A\) would be in \(A\)’s body and \(B\)’s body
    • \(B\) would be in \(A\)’s body and \(B\)’s body

Non-standard hybridizing

Create your own hybrid theory

Try to create your own hybrid theory that uses the soul theory. Does it solve anything?