Section 4.3You Can’t Step into

the Same River Twice

Self as Process

Thought Experiment: Shoemaker’s Brain Transplant

• Suppose that it’s possible to perform brain transplants.

• Suppose further that the brains of Brown and Robinson are switched so that Brown’s brain is in Robinson’s body and vice versa.

• Wouldn’t the body with Brown’s brain be Brown?

The Brain Theory

• According to the brain theory, identical persons are those who are psychologically continuous with one another and whose psychology is caused by and realized in the same brain.

Thought Probe: Body Transplants

• Suppose that one day it becomes technically possible to transplant a brain from one body to another.

• Do you believe that your identity go where your brain goes? Why or why not?

Split Brains

• In patients who have undergone “split-brain surgery,” there seems to be two centers of consciousness; “two wills in one cranial vault.”

• So perhaps just as our entire body in not essential to us, neither is our entire brain.

Thought Experiment: Parfit’s Division

• Suppose that Parfit’s brain hemispheres have the same psychology and that Parfit is one of three identical triplets.

• Now suppose that his body is injured as well as the brains of his two identical brothers and that each half of his brain is transplanted into the body of one of his brothers.

• Which of the brothers is Parfit?

Closest Continuer Theories

• Personal identity cannot consist in psychological or physical continuity because identity is a relation that can hold only between a thing and itself.

• To avoid the reduplication problem, it seems that a theory of personal identity must either rule out any sort of splitting, or it must have some means of determining which branch is identical to the original.

Non-branching Theory

• According to the non-branching theory, identical persons are those who are psychologically continuous with one another and whose causal connection has not branched.

• In this view, neither of the surviving triplets would be Parfit.

Thought Probe:Who Is Behind the Hand?

• Roger Sperry’s claim that split-brain operations create “two free wills in one cranial vault” is controversial because these patients often function normally outside of the laboratory.

• However, alien hand syndrome, in which the hand “seems to perform meaningful acts without being guided by the patient,” lends some credence to Sperry’s claim.

• Could the agent behind an alien hand be a person? How could we tell?

Closest Continuer Theory

• According to the closest continuer theory, identical persons are those who are closest continuers of one another.

• In this view, neither of the surviving triplets would be identical to Parfit because they are both equally close continuers.

The Only X and Y Principle

• According to the only x and y principle, whether one thing, x, is identical to another thing, y, can depend only on facts about x and y.

• Both the non-branching theory and the closest continuer theory reject this principle.

Thought Probe: Branch Lines

• Should we reject the only x and y principle?• If someone were to murder one of the two

surviving triplets, the closest continuer theory would have us believe that the lone surviving triplet is now identical to Parfit.

• Is that plausible?

Identity and What Matters in Survival

• It’s commonly assumed that we can survive the death of our bodies only if we’re numerically identical to someone who exists after our body dies.

• Perhaps all that is needed for survival is psychological continuity.

Identity and What Matters in Responsibility

• It’s commonly assumed that we can be held responsible for an action only if we are numerically identical to the person who performed it.

• Perhaps all that is needed for responsibility is psychological continuity.

Thought Experiment: Parfit’s Reformed Nobelist

• “Suppose that a man aged ninety, one of the few rightful holders of the Nobel Peace Prize, confesses that it was he who, at the age of twenty, injured a policeman in a drunken brawl.”

• Should we now punish him for that crime?

Explaining the Self

• We have been unable to find a set of necessary and sufficient conditions for personal identity. Why is that?

• Perhaps the best explanation is that the self is not a thing but a process.

Thought Probe: Robert and Frank

• Suppose that a criminal named Frank changes his name to Robert and changes his personality, beliefs, attitudes and desires.

• Should Robert be punished for what Frank did?

Moral Agents, Narratives, and Persons

• Only those persons who have the concepts of rights and wrong and can act on those concepts are held accountable for what they do.

• These people are known as “moral agents.”

• For example, the very young, the mentally incapacitated, and the insane may not be moral agents.