Thought experiments are basically devices of the imagination. They are employed for various purposes such an entertainment, education, conceptual analysis, exploration, hypothesizing, theory selection, theory implementation, etc. Some applications are more controversial than others. Few would object to thought experiments that serve to illustrate complex states of affairs, or those that are used in educational contexts. The situation is different, however, with respect to the appropriation of imagined scenarios to investigate reality (very broadly conceived to include things like electrons, tables, rain, beliefs, morals, people, numbers, universes, and even divine beings). It is this use of thought experiments that attracts most of the attention inside and outside of philosophical discourse. Significant is the overlap here with many other central philosophical topics, such as the nature of the imagination, the importance of understanding in contrast to explanation, the role of intuition in human cognition, and the relationship between fiction and truth. Moreover, thought experiments are interdisciplinary in two important respects. Firstly, not only philosophers study them as a research topic, but also historians, cognitive scientists, psychologists, etc. Secondly, they are used in many disciplines, including biology, economics, history, mathematics, philosophy, and physics (although, interestingly, not with the same frequency in each).
Most often thought experiments are communicated in narrative form, frequently with diagrams. It is important to distinguish between the imagined scenarios that are featured in thought experiments, on the one hand, and the narratives that establish the scenarios in people’s mind, on the other. Once a scenario is imagined it may assume a life on its own, and this explains partly the creative power of a good thought experiment. Experimental results may obtain that actually run counter to the narrative that initiated the discussion of an imagined scenario. Besides, 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, though there may be some overlap. They should also be distinguished from counterfactual reasoning in general, as they seem to require an experimental element, which explains the impression that something is experienced in a thought experiment (i.e., being seen, felt, heard, etc.; not literally, of course). In other words, though many call any counterfactual or hypothetical situation a thought experiment (see, e.g., Rescher 1991), this appears too encompassing. It is a quite different matter as to whether there is a logical structure common to all of thought experiments. Based on considerations of logical structure, a taxonomy has been proposed according to which all thought experiments fall into two classes: “Necessity Refuters” and “Possibility Refuters” (see Sorensen 1990, 132–160). Such proposals especially fuel the debate about identity conditions of thought experiments. What modifications to logical structure does a thought experiment tolerate before it ceases to exist and a new one is born? In other words, how much emphasis on propositional characteristics is appropriate in the analysis of thought experiments?
Rescher, Nicholas, 1991, “Thought Experiments in Presocratic Philosophy”, in T. Horowitz and G. Massey (eds.), Thought Experiments in Science and Philosophy, Lanham: Rowman & Littlefield, 31–42.
Sorensen, Roy A., 1992a, Thought Experiments, Oxford: Oxford University Press–––, 1992b, “Thought Experiments and the Epistemology of Laws”, Canadian Journal of Philosophy, 22: 15–44. –––, 1992c, “Moral Dilemmas, Thought Experiments, and Concept Vagueness”, Philosophical Studies, 63: 291–308. –––, 2011, “Das Chinesische Musikzimmer”, Deutsche Zeitschrift für Philosophie, 59: 61–63.