The opening of Sraffa’s Archives has given the opportunity to unveil what is behind the published works, giving clues to interpret them. Among the contributions which are found in his unpublished papers, there are those related to Sraffa’s challenge to causality in economics. In this paper, co-authored with Annalisa Rosselli, we argue that Sraffa’s entire research project is a struggle to escape from mechanical, i.e. causal theory, and to develop a geometrical representation of the economic structure. While a geometrical theory refers to an instant in time and is concerned with logical relations, a mechanical theory refers to processes that happen in real time, in which causality is involved. The reasons why he embarked in such a project are complex and possibly related to his early beliefs that the requirements for causal explanations – like those which are met in physics – are too stringent to be applicable in economics, whose causes are often of metaphysical (and therefore ideological) nature. Unlike neoclassical economics, Sraffa held that change in economic realities hardly ever manifested itself in the form of infinitesimal variations in magnitudes that leave the overall structure unchanged. In that approach, change is required to find the marginal product (or utility) upon which supply and demand curves are derived and price and quantity are determined both in a given market on a given instant and at different times. The well-known passage in the Preface to Production of Commodities: “The investigation is concerned exclusively with such properties of an economic system as do not depend on changes in the scale of production or in the proportions of ‘factors’” (Sraffa 1960, v) can be better understood in the light of the above arguments. The issue is the difference between two instants (in which time is absent) and a change that takes place through time. By keeping change out of the scope, he was keeping the notion of causation out of his project of building a geometrical description of the economic system.