 What we might term “experimentalism” encompasses a wide range of different approaches which all assume that thought experiments are a “limiting case” of ordinary experiments. Experimentalism was proposed first by Ernst Mach (1897 and 1905). He defines experimenting in terms of its basic method of variation and its capacity to destroy prejudices about nature. According to Mach, experimenting is innate to higher animals, including humans. The thought experiment just happens on a higher intellectual level but is basically still an experiment. At the centre of thought experimenting is a “Gedankenerfahrung”, an experience in thought. Such an experience is possible because thought experiments draw from “unwillkürliche Abbildungen von Tatsachen” (non-arbitrary images of facts) acquired in past experiences of the world. Some thought experiments are so convincing in their results that an execution seems unnecessary; others could be conducted in a real-world experiment, which is the most natural trajectory of a scientific thought experiment. In any case thought experiments can result in a revision of belief, thereby demonstrating their significance for scientific progress. Mach also appreciates the didactic value of thought experiments: they help us to realize what can be accomplished in thinking and what cannot.