Carl G. Hempel: Thought Experiments Between Methodological Monism and the Discovery/Justification Dichotomy

Hempel's account of thought experiments has been discussed only by a very few authors and, for the most part, with rather cursory remarks. Its importance, however, is not only historical, but also systematic theoretical, because it involves the distinction between discovery and justification, a main pillar of neopositivistic philosophy of science. Hempel raised the question whether thought experiments constitute a methodological component of scientific research or, on the contrary, are merely a heuristic-psychological device for obtaining and/or transmitting new ideas. While conceding a few exceptions in the natural sciences, he argued that TEs always have a heuristic character in the social sciences. There is however a fundamental tension in Hempel's conception of thought experiments, between the thesis of methodological monism and the neopositivistic dichotomy discovery/justification. On the one hand, on the basis of the unity of scientific method, Hempel admits a difference only in degree between the natural and the human sciences, but on the other hand, he draws a principled distinction between thought experiments of the human sciences (which have only a greater or lesser heuristic value) and those of the natural sciences (which may have also a cognitive-justificatory value). If one assumes the unity of method in the minimal sense in which no scientific knowledge can renounce intersubjective controllability, this tension can be removed either by rejecting the discovery/justification dichotomy or by interpreting it differently. Here, following the second path, two senses of the dichotomy are distinguished, one of which must be accepted, while the other rejected. This removes the internal tension in Hempel's conception of TEs and suggests the thesis that any plausible thought experiment, both in the natural and the human sciences, must already contain some justification, implicit or explicit, of the theoretical hypotheses that they formulate.