Chapter 4 the problem of personal identity
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Chapter 4 The Problem of Personal Identity. The Problem of Change. How can something change and yet remain the same thing? If something changes, it’s different. And if it’s different, it’s no longer the same. Qualitative vs. Numerical Identity.

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Chapter 4 The Problem of Personal Identity

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Chapter 4 the problem of personal identity

Chapter 4The Problem of Personal Identity

The problem of change

The Problem of Change

  • How can something change and yet remain the same thing?

  • If something changes, it’s different. And if it’s different, it’s no longer the same.

Qualitative vs numerical identity

Qualitative vs. Numerical Identity

  • Two objects are qualitatively identical if and only if they share the same properties (qualities); two cue balls from the same manufacturer, for example.

  • Two objects are numerically identical if and only if they are one and the same; Mark Twain and Samuel Clemens, for example.

Accidental vs essential properties

Accidental vs. Essential Properties

  • An accidental property is one that something can lose without ceasing to exist. Your hair being a certain length, for example, is an accidental property of you.

  • An essential property is one that something cannot lose without ceasing to exist. Your being a person, for example, is an essential property of you.

Thought probe a different person

Thought Probe:A Different Person

  • Kathleen Soliah certainly seems to be a qualitatively very different person than she was in the 1970s.

  • Is she numerically different?

  • Is she different enough that she should get a reduced sentence?

Section 4 1 we are such stuff as dreams are made on

Section 4.1We Are Such Stuff asDreams are Made On

Self as Substance

Locke on identity conditions

Locke on Identity Conditions

  • Masses of matter like rocks or lumps of clay retain their identity as long as they retain the atoms out of which they are made.

  • Living things like plants or animals retain their identity as long as they retain their functional organization.

Thought probe hobbes s ship of theseus

Thought Probe: Hobbes’s Ship of Theseus

  • Suppose that the planks in Theseus’s ship have been replaced one by one over the years until none of the original planks remained.

  • Suppose further that the original planks were saved and put back into their original order.

  • Which ship is identical to the original?



  • Persons are generally considered to be rational, self-conscious beings that have free will.

  • They have full moral standing, including the right to life.

Non human persons

Non-human persons

  • According to animalism, there can be no non-human persons.

  • But rational, self-conscious computers, aliens, and animals seem possible.

  • So being a human may not be a necessary condition for being a person.

Thought probe is rachael a person

Thought Probe:Is Rachael a Person?

  • If there were a test for empathic ability or emotional intelligence, would it be a legitimate test for personhood?

  • Why or why not?



  • Animalism is the doctrine that identical persons are identical human animals.

  • According to animalism, once our bodies die, we cease to exist.

  • So our only hope for eternal life is some form of resurrection.

Thought experiment the vegetable case

Thought Experiment:The Vegetable Case

  • Imagine that you lapse into a persistent vegetative state and that as a result your higher cognitive functions are destroyed and that the loss is permanent.

  • Is the human animal that results when the cerebrum is destroyed strictly and literally you, or is it no more you than a statue erected after your death would be you?

Humans who are not persons

Humans Who are Not Persons

  • Those who have fallen into a permanent vegetative state are no longer capable of being rational or self-conscious.

  • Even though they have a living, human body there is reason to think that they are no longer persons.

  • So being a human may not be a sufficient condition for being a person.

Thought probe permanently unconscious

Thought Probe: Permanently Unconscious

  • According to Wikler, Terri Schiavo died in 1980 when she became permanently unconscious.

  • Do you agree that patients who are permanently unconscious have ceased to exist?

  • Should we adopt a higher-brain definition of death?

  • What would be its advantages and disadvantages?

Body switches

Body Switches

  • According to animalism, it’s impossible for one person to inhabit two different bodies.

  • But body switches as portrayed in the movies Big, Heaven Can Wait, All of Me, Freaky Friday, etc., seem possible.

  • So having the same body may not be a necessary condition for being the same person.

Thought experiment locke s tale of the prince and the cobbler

Thought Experiment: Locke’s Tale of the Prince and the Cobbler

  • “For should the Soul of a Prince, carrying with it the consciousness of the Prince’s past life, enter and inform the Body of a Cobbler…every one sees, he would be the same Person with the Prince.”

  • If such body switches are possible, animalism is false.

Thought probe safe cloning

Thought Probe:Safe Cloning

  • “The Raelians eventually hope to develop adult clones into which humans could transfer their brains,” Rael said.

  • Suppose that cloning turns out to be as safe as in vitro fertilization and that the mind transfer produces no ill effects.

  • Would it be wrong to try to achieve immortality this way?

Thought experiment the transplant case

Thought Experiment: The Transplant Case

  • Imagine that an ingenious surgeon removes your cerebrum and implants it into another head.

  • Are you the biologically living but empty-headed human being that has inherited your vegetative functions?

  • Or are you the person who ends up with your cerebrum and your memories?

  • Or are you dead?

Thought experiment unger s great pain

Thought Experiment: Unger’s Great Pain

  • Imagine you’re about to undergo a brain transplant.

  • Unger asks whether you would choose to have yourself suffer considerable pain before the transplant to prevent the person with your brain from suffering even greater pain afterwards.

  • If so, animalism is false.

Siamese twins

Siamese Twins

  • Some Siamese twins have two heads but one body.

  • Is this a counterexample to animalism?

  • Can animalism be modified to account for this counterexample?

Multiple persons one body

Multiple Persons, One Body

  • According to animalism, it’s impossible for one body to contain two persons.

  • But in the case of multiple personality disorder, split-brain patients, and Siamese twins, it seems as if there are two persons in one body.

  • So having the same body may not be sufficient for being the same person.

Soul theory

Soul Theory

  • According the soul theory, identical persons are those with identical souls.

  • As long as your soul exists, you exist.

  • But what are the identity conditions for souls? What is it for one soul to be identical to another soul?

Souls and thoughts

Souls and Thoughts

  • Souls are thinking substances. They are not thoughts; they are things that think.

  • The relation between a soul and its thoughts can be likened to the relation between a pincushion and its pins.

  • Just as a pincushion can have different pins in it at different times, the same soul can have different thoughts in it at different times.

Thought experiment the king of china

Thought Experiment: The King of China

  • Suppose someone offered to make you the King of China on the condition that you lose all of your memories.

  • In such a case, it’s doubtful that you would be around to enjoy the wealth even though, presumably, your soul would be.

  • So having the same soul may not be a necessary condition for being the same person.

Thought experiment nestor and thersites

Thought Experiment: Nestor and Thersites

  • Suppose that all of your thoughts and memories were transferred to a soul that once housed those of Nestor or Thersites.

  • That would not make you identical to Nestor or Thersites.

  • So having the same soul may not be a necessary condition for being the same person.

Kant s soul switch

Kant’s Soul Switch

  • “If…we postulate substances such that the one communicates to the other representations together with the consciousness of them, we can conceive a whole series of substances….The last substance would then be conscious of all the states of the previously changed substances as being its own states.”

  • So identity goes—not where your soul goes—but where your consciousness goes.

Thought probe near death experiences

Thought Probe: Near-Death Experiences

  • Do near-death experiences provide a good reason for believing in the existence of a soul?

  • Psychologists believe that near-death experiences are a form of hallucination.

  • Is that the best explanation of the experiences?

Thought probe souls in heaven

Thought Probe: Souls in Heaven

  • Many of those who believe in souls believe that their souls will go to heaven.

  • What’s heaven like? Will we have bodies in heaven? How old will children be? Will then grow up in heaven? Will anyone age in heaven? Will the blind see and the deaf hear? Will the insane become sane?

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