In his 1931 unpublished “Surplus Product” manuscript Sraffa used an open–closed distinction to explain the relationship between the “economic field” and distribution. This chapter examines Sraffa’s thinking in this regard, and shows how it allowed him to resolve a problem he encountered in his early objectivist representation of commodity production in economies with a surplus. The chapter argues that Sraffa adopted a view different from Bertalanffy’s general systems theory understanding of open and closed systems developed around the same time in such a way as to address the specific nature of economics. The chapter compares two related interpretations of Sraffa’s thinking in regard to the open–closed distinction developed by Arena and Ginzburg, and also addresses how Sraffa’s thinking regarding open and closed systems compares with similar thinking of Wittgenstein and Gramsci. The concluding discussion contrasts Sraffa’s causal reasoning with mainstream economics’ ceteris paribus method of causal reasoning.