Stanford Encyclopedia of Philosophy
Substantive revision on August 12, 2014
Thought experiments are devices of the imagination used to investigate the nature of things. They are used for diverse reasons in a variety of areas, including economics, history, mathematics, philosophy, and the sciences, especially physics. Most often thought experiments are communicated in narrative form, frequently with diagrams. Thought experiments should be distinguished from thinking about experiments, from merely imagining any experiments to be conducted outside the imagination, and from psychological experiments with thoughts. They should also be distinguished from counterfactual reasoning in general, as they seem to require an experimental element, which seems to explain the impression that something is experienced in a thought experiment. In other words, though many call any counter-factual or hypothetical situation a thought experiment, this seems too encompassing. It seems right to demand that they also be visualized (or perhaps smelled, tasted, heard, touched); there should be something experimental about a thought experiment.
The primary philosophical challenge of thought experiments is simple: How can we learn about reality (if we can at all), just by thinking? More precisely, are there thought experiments that enable us to acquire new knowledge about the intended realm of investigation without new empirical data? If so, where does the new information come from if not from contact with the realm of investigation under consideration? Finally, how can we distinguish good from bad instances of thought experiments? These questions seem urgent with respect to scientific thought experiments, because most philosophers and historians of science “recognize them as an occasionally potent tool for increasing our understanding of nature. […] Historically their role is very close to the double one played by actual laboratory experiments and observations. First, thought experiments can disclose nature's failure to conform to a previously held set of expectations. Second, they can suggest particular ways in which both expectation and theory must henceforth be revised.” (Kuhn, 1977, p. 241 and 261) The questions are urgent regarding philosophical thought experiments, because they play an important role in philosophical discourse. Philosophy without thought experiments seems almost hopeless.
There is widespread agreement that thought experiments play a central role both in philosophy and in the natural sciences. General acceptance of the importance of some of the well-known thought experiments in the natural sciences, like Maxwell's demon, Einstein's elevator or Schrödinger's cat. Probably more often than not, these, and many other thought experiments have led the careful analysis of their epistemic powers to the conclusion that we should not portray science as an exclusively empirical activity (see Winchester, 1990, p. 79).
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