Thought experiment

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A thought experiment (from the German term Gedankenexperiment, coined by Ernst Mach) in the broadest sense is the use of an imagined scenario to help us understand the way things really are. The understanding comes through reflection on the scenario. Thought experiment methodology is a priori, rather than empirical, in that it does not proceed by observation or experiment.

Thought experiments have been used in philosophy, physics, and other fields. They have been used to pose questions in philosophy at least since Greek antiquity, some pre-dating Socrates. In physics and other sciences many famous thought experiments date from the 19th and especially the 20th Century, but examples can be found at least as early as Galileo.

1 Thought experiments in philosophy
2 Thought experiments in physics
3 Famous thought experiments
4 Books about thought experiments
5 External links

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Thought experiments in philosophy

In philosophy, a thought experiment typically presents an imagined scenario with the intention of eliciting an intuitive response about the way things are in the thought experiment. (Philosophers might also supplement their thought experiments with theoretical reasoning designed to support the desired intuitive response.) The scenario will typically be designed to target a particular philosophical notion, such as morality, or the nature of the mind or linguistic reference. The intuitive response to the imagined scenario is supposed to tell us about the nature of that notion in any scenario, real or imagined.

For example, a thought experiment might present a situation in which an agent intentionally kills an innocent for the benefit of others. Here, the relevant question is whether the action is moral or not, but more broadly whether a moral theory is correct that says morality is determined solely by an action’s consequences. John Searle imagines a man in a locked room who receives written sentences in Chinese, and returns written sentences in Chinese, according to a sophisticated instruction manual. Here, the relevant question is whether or not the man understands Chinese, but more broadly, whether a functionalist theory of mind is correct.

It is generally hoped that there is universal agreement about the intuitions that a thought experiment elicits. (Hence, in assessing their own thought experiments, philosophers may appeal to “what we should say,” or some such locution.) A successful thought experiment will be one in which intuitions about it are widely shared. But oftentimes, philosophers differ in their intuitions about the scenario.

The scenario presented in the thought experiment must be possible in some sense. In many thought experiments, the scenario would be possible according to the laws of nature, or nomologically possible. John Searle’s Chinese Room is nomologically possible. Some thought experiments present scenarios that are not nomologically possible. In his Twin Earth thought experiment, Hilary Putnam asks us to imagine a scenario in which there is a substance with all of the observable properties of water (e.g., taste, color, boiling point), but which is chemically different from water. It has been argued that this thought experiment is not nomologically possible, although it may be possible in some other sense, such as metaphysical possibility. It is debatable whether the nomological impossibility of a thought experiment impugns its supposed intuitive results.

Other uses of imagined scenarios arguably are thought experiments also. In one use of scenarios, we might imagine persons in a particular situation (maybe ourselves), and ask what they would do. John Rawls asks us to imagine a group of persons in a situation where they know nothing about themselves, and are charged with devising a social or political organization. The various uses of the state of nature, as by Thomas Hobbes and John Locke may also be considered thought experiments.

The use of thought experiments in philosophy has been criticized by some philosophers, especially in the philosophy of mind. Daniel Dennett has derisively referred to thought experiments as "intuition pumps." One criticism that has been voiced is that some science fiction-type thought experiments are too wild to yield clear intuitions, or that any resulting intuitions could not possibly pertain to the real world. Another criticism is that philosophers have used thought experiments (and other a priori methods) in areas where empirical science should be the primary method of discovery, as for example, with issues about the mind.

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Thought experiments in physics

Thought experiments in physics are intended to give us a priori knowledge of the natural world, rather than apriori knowledge of our concepts, as philosophy tries to do.

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