This article contributes to theoretical debate on whether J.R. Commons's Institutional Economics (1934) contains the framework of cumulative causation between “customs” in societies and “habitual assumptions” of individuals. The central issue of the argument can be reduced to the extent to which Commons accepted the psychology of the pragmatist J. Dewey. Therefore, the method of discussion for this article is to assess Commons's 1934 manuscripts thoroughly in order to clarify the shift of his approach to Dewey from the pragmatists C.S. Peirce and W. James. Having checked the literature, it is confirmed that Commons's approach to pragmatism shifted across the ages. In addition, to find elaborate explanations of “habitual assumptions,” which is a key concept of cumulative causation, the sections endorsing Dewey's perspective should be consulted. In doing so, this article proves that Commons (1934) contains descriptions explaining the framework of cumulative causation appropriately. However, its psychological foundation is not “instinct–habit psychology” but “fundamental wishes–habitual assumptions psychology.”