My interest in contemporary philosophy focuses on language and lived subjective experiences. In looking further into the development of our discussion about thought experiments lets examine the past thirty years or so. It is fair to say that Gendankens or thought experiments were primarily an important topic in the philosophy of science and the philosophy of philosophy (“metaphilosophy”), before the scope widened up at a later point.
There is a simple reason for that path. At the core of the discussion sits a relatively simple epistemological challenge that is presented in a particularly powerful manner by numerous thought experiments that the history of science has to offer. They suggest that we can learn about the real world by virtue of merely thinking about imagined scenarios. But how can we learn about reality (if we can at all), just by thinking?
Are there really thought experiments that enable us to acquire new knowledge about nature without new empirical data? If so, where does the new information come from? Finally, how can we distinguish good from bad instances of thought experiments? These questions seem urgent with respect to scientific thought experiments, because many “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). Yet, questions surrounding the epistemological challenge that certain scientific thought experiments pose, are equally urgent with respect to thought experiments outside of the natural sciences. This is especially true with respect to philosophy itself. Philosophy offers numerous examples of thought experiments that play a role similar in importance to some scientific thought experiments. And this fact provokes in turn further inquiries into the relationship between the natural sciences and philosophy, especially with respect to phenomena that implicate both the natural sciences and philosophy, such as the mind and free will (see, e.g., Wilkes 1988; Young 2013).
If scientific practice has room for thought experiments, then the question arises as to why we would want philosophical methodology to be more discriminatory in this respect. One reason that is often offered is that results of scientific thought experiments may be subjected to further empirical testing. Obviously, this can’t be done for philosophical thought experiments. But, it seems difficult to accept a categorical separation of science and philosophy along these lines. The 17th century saw some of the most brilliant practitioners of thought experimentation in Galileo, Descartes, Newton, and Leibniz, all of whom pursued the project of “natural philosophy.” And in our own time, the creation of quantum mechanics and relativity are almost unthinkable without the crucial role played by thought experiments, most of which relate to important philosophical issues that arise from these scientific theories. Besides, much of ethics, philosophy of language, and philosophy of mind is based on the results of thought experiments in a way that seems very similar to scientific thought experiments (though some might contest this), including Searle’s Chinese room, Putnam’s twin earth, and Jackson’s Mary the colour scientist. Philosophy, even more than the sciences, would be severely impoverished without thought experiments. These observations partly explain why it has been argued that a more “unified” account of thought experiments is desirable (see Boniolo 1997; Cooper 2005, pp. 329–330; Gähde 2000). Of course, it is important not to downplay the significant differences between the sciences and philosophy. But an account of thought experiments seems more powerful if it can do justice to the fact that not only in the sciences we find many of them.
There have been several attempts to define “thought experiment” along the lines of traditional conceptual analysis (see, e.g., Picha 2011; McComb 2013), but likely it will be better to leave the term loosely characterized, so as not to prejudice the ongoing investigation. Of course, we need to have some idea as to what thought experiments are to guide a proper philosophical analysis (see Häggqvist 2009), but this does not mean that we need to begin with a technical definition, specifying necessary and sufficient conditions. In fact, many of the most important concepts we deal with remain rather loosely defined when philosophical inquiry begins, e.g., religion or democracy. Luckily, there are plenty of examples to refer to in order to circumscribe our subject matter well enough. As well as those already mentioned, there are Newton’s bucket, Heisenberg’s gamma-ray microscope, Einstein’s elevator, Leibniz’s mill, Parfit’s people who split like amoebas, and Thomson’s violinist.
Everyone is probably familiar with some of these. Less familiar thought experiments include the mouse that breaks into the tabernacle of a medieval Roman Catholic Church building to feed on the consecrated wafers kept in there (see Fehige 2011). Roman Catholic Christians believe that a consecrated wafer is the body of Christ. The “substance” of the wafer, understood in terms of Aristotelian categories, is believed to be replaced. In its place is the “substance” of Christ’s body after consecration by a priest. Only the Aristotelian “accidents” of the wafer remain intact (smell, colour, texture, etc.). Does the mouse eat the body of Christ (if any human actually does)? Another example less known example is “the dome” thought experiment, which is to prove indeterminism in Newtonian physics. Imagine a mass sitting on a radially symmetric surface in a gravitational field. Guided by Newton’s laws of motion one comes to realize that the mass can either remain at rest for all times, or spontaneously move in an arbitrary direction (see Norton 2008). This thought experiment triggers a number of very interesting questions concerning the nature of Newtonian theory, the meaning of “physical”, and the role of idealizations in physics. And, of course, does it show what it claims? (see Malament 2008).
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