The Polish logician Stanisław Leśniewski (1886–1939) must surely count as the father of mereology—the theory of parts and wholes—but around 1930, Goodman re-invents the theory together with his fellow graduate student Henry S. Leonard (1905–1967). Only in 1935 do Goodman and Leonard learn of Leśniewski’s work through one of their fellow students, W.V.  Quine (Quine 1985, 122). An early version of Leonard and Goodman’s system is contained in Leonard’s Ph.D. thesis, Singular Terms (Leonard 1930). In 1936, Leonard and Goodman present their mature system at a meeting of the Association of Symbolic Logic; the corresponding paper is published four years later under the title “The Calculus of Individuals and Its Uses” (Leonard and Goodman 1940). Subsequently, Goodman uses the calculus in his own Ph.D. thesis, A Study of Qualities (SQ), and a version of it in The Structure of Appearance (SA). Little is known about the nature of Goodman and Leonard’s cooperation on the calculus. Goodman attributes the first thought for the collaborative project to Leonard (PP, 149). Leonard, more concretely, suggests in a (still) unpublished note: