Résumé
In his book Des sciences physiques aux sciences morales (1922), Rueff recommends the "scientific" method (from physical science) and which, applied to political economics, strengthens its rational feature while giving a special place on observation. In order to have the most significant example of this, it must wait his unemployment theory. From statistical series, Rueff brings to light that since 1921 a long-term and unexpected unemployment had developed in England. He deduces a relation between the unemployment rate and the real wage rate, which he wants then to explain in order to establish causes and build the theory of phenomenon.