In the preface of the Philosophical Investigations, Wittgenstein says that his “most fruitful ideas” are due to the stimulus of Sraffa's criticism, but Sraffa is not mentioned anywhere else in the book. It remains a puzzle in the literature how and why Sraffa influenced Wittgenstein. This paper presents a solution to this puzzle. Sraffa's criticism led Wittgenstein away from the calculus conception of language of the Big Typescript (arguably, an adaptation of the calculus of the Tractatus), and towards the “anthropological (...) view,” which structures both the opening sections of the Philosophical Investigations and Wittgenstein's later philosophy of mathematics. (shrink)