On Possibilities and Thought Experiments∗

This paper concerns two related recent books by Nicholas Rescher, Imagining Irreality on possibilities and What If? on thought experiments—see [23] and [24]. The books are related because a theory on thought experiments presupposes a theory on possibilities. The effect of this and of the fact that they have a wider range of application than thought experiments will be that possibilities will receive the bulk of the attention. The books are also very different. A view on possibilities is unavoidably highly theoretical and sophisticated. It involves a host of arguments that pertain to ontology, epistemology, and language. A theory of thought experiments, to the contrary, mainly concerns a matter of reasoning. Everyone competent in the domain to which the thought experiment belongs is able to assess its soundness. While the resulting theory may be sophisticated, its subject matter belongs, from a philosopher’s point of view, to a practical realm. On both subjects, Rescher offers a theory that is systematic and embracing. With respect to possibilities, he takes a straight linguistic stand, heavily attacking the reifying views that came into fashion at the end of the twentieth century. The book on thought experiments concentrates on their use in philosophy without avoiding other domains or general characteristics. It presents an comprehensive theory, illustrated by many examples, that deals with an impressive number of aspects. These aspects are handled in a way that does right to sophistication but never gives in on the perspicuity that is so typical for Rescher. A particular strength of both theories is that they are embedded into a larger view that was developed against a broad background in the history of philosophy, present-day systematic philosophy, as well as the contemporary sciences. The reader should not expect an attack on Rescher’s position. Mainly through the influence of Leo Apostel, the nominalistic and conceptualistic critique of platonistic constructions and the constructivist critique of mathematical realism played a pivotal role in my philosophical upbringing. Moreover, from