Thought Experiments

A thought-experiment is a hypothetical scenario set forth as a puzzlement or a basis for argument

Thought Experiments
  • A thought-experiment is a hypothetical scenario set forth as a puzzlement or a basis for argument.
  • A classic example is Einstein’s Falling Elevator Gedankenexperiment, which he said led him to his theory of gravitation.
  • Philosophers also use thought experiments.
Judith Jarvis Thomson’s Famous Violinist
  • Since Roe v. Wade was overturned, at least ten states have banned abortion with no exceptions for rape or incest. But in 1971 JJ Thomson presented a plausible argument that abortion in the case of rape is morally justified, even if the fetus is a person.
  • Thomson used a thought experiment as the basis for arguing that abortion in the case of rape is morally permissible even assuming that the fetus is a person.
    • “You wake up in the morning and find yourself back to back in bed with an unconscious violinist. A famous unconscious violinist. He has been found to have a fatal kidney ailment, and the Society of Music Lovers has canvassed all the available medical records and found that you alone have the right blood type to help. They have therefore kidnapped you, and last night the violinist’s circulatory system was plugged into yours, so that your kidneys can be used to extract poisons from his blood as well as your own. [Unplugging him now would kill him; but in nine months] he will have recovered from his ailment, and can safely be unplugged from you. ”
      • “A Defense of Abortion” Philosophy & Public Affairs , 1971
  • Thomson argues that, since the situation was forced on you, you have no moral obligation to keep the violinist attached. What if, she asks, it were nine years rather than nine months, or the rest of your life in bed?
  • By analogy, Thomson argues, a woman who’s pregnant because of rape has no moral obligation to carry the fetus to term.
Derek Parfit’s Split Brain
Parfit’s Thought Experiment
  • Preliminary Thought Experiment #1: Brain Transplant
    • Suppose first that I am one of a pair of identical twins, and that both my body and my twin’s brain have been fatally injured. Because of advances in neurosurgery, it is not inevitable that these injuries will cause us both to die. We have between us one healthy brain and one healthy body. Surgeons can put these together.
  • Preliminary Thought Experiment #2: Hemispherectomy
    • There are many people who have survived, when a stroke or injury puts out of action one of their hemispheres. With his remaining hemisphere, such a person may need to re-learn certain things, such as adult speech, or how to control both hands. But this is possible. In my example I am assuming that, as may be true of certain actual people, both of my hemispheres have the full range of abilities. I could thus survive with either hemisphere, without any need for re-learning.
        • Hemispherectomy is a very rare neurosurgical procedure in which a cerebral hemisphere (half of the upper brain, or cerebrum) is removed, disconnected, or disabled.
  • Preliminary Thought Experiment #3: Hemispherectomy + Half-Brain Transplant
    • I shall now combine these last two [thought experiments]. I would survive if my brain was successfully transplanted into my twin’s body. And I could survive with only half my brain, the other half having been destroyed. Given these two facts, it seems clear that I would survive if half my brain was successfully transplanted into my twin’s body, and the other half was destroyed.
  • Final Thought Experiment: Hemispherectomy +  Two Half-Brain Transplants
    • My body is fatally injured, as are the brains of my two brothers. My brain is divided, and each half is successfully transplanted into the body of one of my brothers. Each of the resulting people believes that he is me, seems to remember living my life, has my character, and is in every other way psychologically continuous with me. And he has a body that is very like mine.
    • So what happened to me?
      • I did not survive
      • I survived as one of the two people
      • I survived as both.
No Possibility Makes Sense
  • There are only four possibilities:
    • (1) I do not survive;
    • (2) I survive as one of the two people;
    • (3) I survive as the other;
    • (4) I survive as both.
  • The objection to (1) is this. I would survive if my brain was successfully transplanted. And people have in fact survived with half their brains destroyed. Given these facts, it seems clear that I would survive if half my brain was successfully transplanted, and the other half was destroyed. So how could I fail to survive if the other half was also successfully transplanted? How could a double success be a failure?
  • Possibilities (2) and (3) are that I shall be one of the two resulting people. The objection here is that, in this case, each half of my brain is exactly similar, and so, to start with, is each resulting person. Given these facts, how can I survive as only one of the two people? What can make me one of them rather than the other?
  • Possibility (4). The problem with double survival is that it does not fit the logic of identity. I and the two resulting people cannot be one and the same person. Since I cannot be identical with two different people, and it would be arbitrary to call one of these people me, we can best describe the case by saying that neither will be me.
Nature of Persons
  • Entity Theory of Persons:
    • A person is a separately existing entity, distinct from their brain and body, and their experiences. The best-known version of this view is that person is a Cartesian Ego.
  • Reductionist Theory of Persons (Parfit’s View)
    • A person is distinct from their brain and body, and their experiences. But they are not separately existing entities. The existence of a person, during any period, just consists in the existence of their brain and body, and the thinking of their thoughts, and the doing of their deeds, and the occurrence of many other physical and mental events.
    • Consider a political party which splits and becomes two rival parties. We can ask, ‘Did the original party cease to exist, or did it continue to exist as one or other of the resulting parties?’ But we do not believe that this is a real question, about different possibilities, one of which must be what happened. This question is empty. Political parties exist.  But they are not separately, or independently, real.
    • As with political parties, the question of what happens to me in Parfit’s thought experiment is not “a real question, about different possibilities, one of which must be what happened.” A person is not an entity whose existence is separate from the existence of their brain and body, and the occurrence of their experiences. 
Anatta / Anatman
    • In Buddhism, Anatta is the doctrine that there is in humans no permanent, underlying substance that can be called the soul.
    • The Buddha rejected the existence of the soul as a metaphysical substance, though he recognized the existence of the self as the subject of action in a practical and moral sense. Life is a stream of becoming, a series of manifestations and extinctions. The concept of the individual ego is a popular delusion; the objects with which people identify themselves — fortune, social position, family, body, and even mind — are not their true selves. There is no permanent, underlying self.
    • To make clear the concept of no-self (anatman), Buddhists set forth the theory of the five constituents (khandhas) of human existence:
      • (1) corporeality or physical forms (rupa),
      • (2) feelings or sensations (vedana),
      • (3) ideations (sanna),
      • (4) mental formations or dispositions (sankhara), and
      • (5) consciousness (vinnana).
    • Human existence is only a composite of the five aggregates, none of which is the self or soul. A person is in a process of continuous change, and there is no fixed underlying entity.
Hume’s Bundle Theory
    • The Bundle theory was advanced by David Hume to the effect that the mind is merely a bundle of perceptions without deeper unity or cohesion, related only by resemblance, succession, and causation. Hume’s well-argued denial of a substantial or unified self precipitated a philosophical crisis from which Immanuel Kant sought to rescue Western philosophy.
  • A Treatise of Human Nature, David Hume, 1739–40
    • For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe any thing but the perception. 
    • When my perceptions are remov’d for any time, as by sound sleep; so long am I insensible of myself, and may truly be said not to exist. And were all my perceptions remov’d by death, and cou’d I neither think, nor feel, nor see, nor love, nor hate after the dissolution of my body, I shou’d be entirely annihilated, nor do I conceive what is farther requisite to make me a perfect non-entity. 
    • If any one upon serious and unprejudic’d reflexion, thinks he has a different notion of himself, I must confess I can reason no longer with him. All I can allow him is, that he may be in the right as well as I, and that we are essentially different in this particular. He may, perhaps, perceive something simple and continu’d, which he calls himself; tho’ I am certain there is no such principle in me… But setting aside some metaphysicians of this kind, I may venture to affirm of the rest of mankind, that they are nothing but a bundle or collection of different perceptions, which succeed each other with an inconceivable rapidity, and are in a perpetual flux and movement.
Reductionist and Entity Theories of Persons
Brain in a Vat
  • You have undergone an operation in which your brain is removed and stored in a vat of nutrients that keeps it alive. The nerve endings of your brain are connected to a supercomputer that runs a program sending electrical impulses that stimulate the brain in the same way that brains are stimulated when perceiving external objects. So your conscious experiences are indistinguishable from the experiences you had before the operation. But you no longer have a body or see real objects or converse with other people, though it seems you do.
  • Argument for skepticism about the external world.
    • If you have no more evidence for one of two competing hypotheses than for the other, it’s irrational to believe either.
    • You have no more evidence that you see real objects than you are a brain-in-a-vat, since you have exactly the same sensations.
    • Therefore it’s irrational for you to believe you see real objects.
Living Neurons Replaced with Synthetic Neurons
  • The human nervous system consists of billions of neurons that affect on another through molecules transmitted across synapses. When sufficient neurotransmitters are received at its input end, a neuron “fires” by sending a reversing voltage down its axon, releasing neurotransmitters at its output end.
  • Suppose scientists develop a synthetic neuron, functionally equivalent to a living neuron, by replacing the nucleus with a microchip and replacing the cell wall and other parts with silicon-based analogs.
  • The synthetic neurons are used, successfully, to replace damaged parts of people’s brains.
  • Suppose all of person’s living neurons are gradually replaced by synthetic neurons, leaving the person with a completely synthetic brain. Is the person conscious like a person with a normal living brain? Or is the “person” no more conscious than a sophisticated robot?
John Rawls’ Original Position
  • Suppose you belong to a group responsible for determining the basic principles of government. So that the selection of the principles won’t be influenced by self-interest, imagine no one in the group knows anything about him or herself: gender, race, religion, age, intelligence, ethnicity, physical appearance, genetic makeup, natural abilities and disabilities, health, social or economic class, wealth, income, talents, etc. Behind this veil of ignorance, what basic principles of government would rational people acting in their own interest agree on?
  • Rawls argues people would agree on the following principles:
    • Each person has an equal right to the most extensive basic liberty compatible with a similar liberty for others.
    • Social and economic inequalities are arranged so that they are both
      • to the greatest benefit of the least advantaged
        • this is the Difference Principle
      • attached to offices and positions open to all under conditions of fair equality of opportunity.
  • Rationale for the Difference Principle:
    • Since a person’s natural talents and the socioeconomic circumstances in which he is born and raised are not his doing and beyond his control, “those who have been favored by nature, whoever they are, may gain from their good fortune only on terms that improve the situation of those who have lost out.” (John Rawls, A Theory of Justice, Page 101)
  • Britannica Political Philosophy
    • Why suppose with Rawls that justice requires an approximately egalitarian redistribution of social and economic goods? After all, a person who prospers in a market economy might plausibly say, “I earned my wealth. Therefore, I am entitled to keep it.” But how one fares in a market economy depends on luck as well as effort. There is the luck of being in the right place at the right time and of benefiting from unpredictable shifts in supply and demand, but there is also the luck of being born with greater or lesser intelligence and other desirable traits, along with the luck of growing up in a nurturing environment. No one can take credit for this kind of luck, but it decisively influences how one fares in the many competitions by which social and economic goods are distributed. Indeed, sheer brute luck is so thoroughly intermixed with the contributions one makes to one’s own success (or failure) that it is ultimately impossible to distinguish what people are responsible for from what they are not. Given this fact, Rawls urges, the only plausible justification of inequality is that it serves to render everyone better off, especially those who have the least.