Introduction : Malaise dans la science économique ?

This is the introductive chapter to the book "Wassily Leontief and Economics", published in February 2019 (ENS editions). Economists produce their statements and forecasts from devices articulating abstract theories with mathematical models and statistical instruments of measurement. What is the empirical significance of these theories, models and instruments? We consider this question from the reflection of Wassily Leontief, 1973 Nobel Prize winner, on the role of mathematics and statistical analysis in economics. His perspective makes it possible to reconsider why, in economics, "the connection does not go by itself" between the theory and the observation, according to the expression of Alain Desrosières. We reconstruct Leontief’s methodology of economics as an empirical science. From there, we show how the input-output device paves the way to empirical and disaggregated macroeconomics.