Abstract

Common opinion ascribes to Immanuel Kant the view that psychology cannot become a science properly so called, because it cannot be mathematized. It is equally common to claim that this reflects the state of the art of his times; that the quantification of the mind was not achieved during the eighteenth century, while it was so during the nineteenth century; or that Kant's so-called “impossibility claim” was refuted by nineteenth-century developments, which in turn opened one path for psychology to become properly scientific. These opinions are often connected, but they are misguided nevertheless. In Part I, I show how the issue of a quantification of the mind was discussed before Kant, and I analyze the philosophical considerations both of pessimistic and optimistic authors. This debate reveals a certain progress, although it remains ultimately undecided. In Part II, I present actual examples of measuring the mind in the eighteenth century and analyze their presuppositions. Although these examples are limited in certain ways, the common view that there was no such measurement is wrong. In Part III, I show how Kant's notorious “ impossibility claim” has to be viewed against its historical background. He not only accepts actual examples of a quantitative treatment of the mind, but also takes steps toward an explanation of their possibility. Thus, he does not advance the claim that the mind as such cannot be mathematized. His claim is directed against certain philosophical assumptions about the mind, assumptions shared by a then-dominating, strongly introspectionist conception of psychology. This conception did and could not provide an explanation of the possibility of quantifying the mind. In concluding, I reflect on how this case study helps to improve the dispute over when and why psychology became a science.