Gaston Milhaud (1858–1918) was a French modern philosopher, who, having started from mathematics, came to philosophy (especially epistemology) and history of science. His works on the history of science were devoted to Greek science and modern science. Milhaud in his papers claimed that important concepts and principles of science (in different disciplines) result from decisions that simultaneously transcend both experience and logic. He emphasized the role of free creation and activity of the mind. The author discusses central problems of Milhaud’s thought, especially the problem of the relationship between science and philosophy.

I give arguments supporting the claim that one of the most prominent methodological results of French conventionalism – rejection of the possibility of a crucial experiment in mature empirical sciences – was formulated simultaneously by Pierre Duhem and Gaston Milhaud in 1894. Thus, I attempt to question the standard approach in philosophy and methodology of science, which attributes the said result exclusively to Duhem. I am building my case of Milhaud’s true contribution to the debate on the rejection of the existence of the experimentum crucis, made in his PhD thesis Essai sur les conditions et les limites de la certitude logique.