More than just a great theoretician, Canguilhem was one of the few philosophers of the 20th century to develop an approach that was shaped by a medical education. He helped define a method of studying the history of science which was practical and rigorous. His work focused on the one hand on the concepts of "normal" and "pathological" and, on the other, a critical history of the formation of concepts such as "reflex" in the history of science. Canguilhem was also a mentor to several French scholars, most notably Foucault, for whom he served as a sponsor in the presentation of "Histoire de la folie à l'âge classique" ("History of Madness") for the "Doctorat d'État" and whose work he followed throughout the latter's life.