ABSTRACT
This chapter discusses focuses the philosophy of applied mathematics used by Leon Walras in his unique defence of his theoretical economics. It introduces three phases in the Walras-Poincare correspondence: the mathematisation of economics; the measurement of utility; Poincare's hierarchy of reservations. The chapter follows with an elaboration of Walras' scientific realist reading of theoretical economics in light of his scientific realist reading of the principles of mechanics. It focuses on Walras' Platonic realism and his essentialist scientific realism. Twenty-seven years later all was not well for Walras' programme of the mathematisation of 'the very foundation of the whole edifice of economics' among various French mathematicians, particularly those open to the use of mathematics in economics. The distinguished French mathematician Hermann Laurent had an extensive correspondence with Walras. The chapter concludes by comparing and contrasting Walras' scientific realist reading of the principles with Poincare's alternative explanation of the robustness of such principles.
