Section 1.3The Laboratory of the Mind

Thought Experiments

Philosophical Theories andThought Experiments

• Philosophical theories explain how it’s possible (or why it’s impossible) for a concept to apply by identifying the conditions for applying it.

• Thought experiments test such theories by determining whether the conditions identified are necessary or sufficient.

Thought Probe: Platonic Humans

• Plato once claimed that human beings are featherless bipeds (creatures that walk on two legs).

• Can you conceive of a featherless biped that is not a human being or a human being that is not a featherless biped?

Aristotle’s Human Being

• According to Aristotle, human beings are rational animals.

• To test this theory, we must derive a test implication. We need determine whether all and only human beings are rational animals.

• Thought experiment: Can you think of any human beings that are not rational animals or vice versa?

Aristotle’s Human Being (revised)

• Test implication: Infants are rational animals. If all and only human beings are rational animals, then infants are rational animals, because infants are human beings.

• Counterexample: Human infants are human beings, but they are not rational.

• Revised theory: All human beings are animals that have the capacity to be rational.

• Thought experiment: Can you conceive of a human being that does not have the capacity to be rational or of a non-human animal that has the capacity to be rational?

Aristotle’s Human Being (revised)

• Our argument against Aristotle goes like this:– (1) If human beings are rational animals, then human

infants must be rational animals. (2) But human infants aren’t rational animals. (3) Therefore it’s not necessarily true that human beings are rational animals.

• The form of this argument is denying the consequent.

Case Study: Explaining How Moral Abortions Are Possible

• Murder is the unjust killing of a person.• So to determine whether abortion is murder,

we have to determine whether a fetus is a person.

Persons

• Persons are beings with full moral rights, including the right to life.

• What makes something a person? Why do normal adult humans have full moral rights but not cows, pigs, and chickens?

Thought Experiment: Warren’s Moral Space Traveler

“Imagine a space traveler who lands on an unknown planet and encounters a race of beings utterly unlike he has ever seen or heard of. If he wants to be sure of behaving morally toward these beings, he has to somehow decide whether they are people, and hence have full moral rights….” What should he look for?

Warren’s Criteria for Personhood

• Consciousness• Reasoning (the developed capacity to solve

new problems)• Self-motivated activity• The capacity to communicate messages of an

indefinite variety of types• Self-consciousness

Thought Probe:The Terri Schiavo Case

• According to Locke and Warren, a person is conscious, self-aware, and capable of reasoning, communicating, and engaging in self-motivated activity.

• If Terri Schiavo was in a persistent vegetative state, and if people in PVS have permanently lost the ability to think, was Terri Schiavo still a person?

• If Terri Schiavo was not a person, was removing the feeding tube an act of murder?

How are thought experiments possible?

• We may have a concept and not be able to state the criteria for applying it.

• Philosophical inquiry tries to make explicit what’s implicit in our understanding of a concept.

• Thought experiments test theories about the conditions under which concepts apply.

Criticizing Thought Experiments

• The value of any experiment is determined by the amount of control with which it is executed.

• If an imaginary situation is not described in sufficient detail, the results of the experiment may be questionable.

• The best way to show that an experiment is unreliable is to conduct a better one.

Conceivability and Possibility

• The best evidence that a situation is possible is that it’s conceivable.

• But from the fact that something seems conceivable, it doesn’t follow that it is conceivable.

• Time travel seems conceivable but isn’t because it leads to a contradiction.

Scientific Thought Experiments

• Any theory that implies a contradiction cannot be true.

• Scientists use thought experiments to test for contradictions.

Thought Experiment: Aristotle’s Theory of Motion

• Aristotle thought that a heavier object would fall faster than a lighter one.

• Imagine that a heavy cannonball is attached to a light musket ball by means of a rope. Now imagine that both this combined system and an ordinary cannonball are dropped from a height at the same time. What will happen?

Thought Experiment: Tooley’s Cat

• Suppose a cat was accidentally given an injection that would cause its brain to develop into one with the same capabilities as ours.

• Would it be wrong to kill the cat before the brain was fully developed?

Thought Experiment: Thomson’s Diseased Musician

• Suppose that a musician with a fatal kidney ailment had his bloodstream attached to yours because you are the only person with the right blood type.

• If you allow him to stay plugged in for nine months, he will lead a normal life.

• Are you morally obligated to stay plugged in?