[Stahl, Leibniz, Hoffmann and breathing].

At the beginning of the XVIII th century, Wilhelm Gottfried Leibniz and Friedrich Hoffmann criticize Georg Ernst Stahl's medical theory. They differenciate between unsound and true reasonings. Namely, they validate Stahl's definition of breath but extracting it from its animist basis and placing it in an epistemology obeying to the principle of sufficient reason and to the mechanical model. The stahlian discovery consists in understanding breath as a calorific ventilation against the ancient conception; the iatromechanists recognize its accuracy, but they try then to transpose it to a mechanical model of ventilation. Using it in a different epistemological context implies that they analyze the idea of discovery "true" in its contents, but "wrong" in its hypothesis. It impels to examine the epistemology of medical knowledge, as science and therapeutics, and in its links with the other scientific theories. Thus, if Leibniz as philosopher and Hoffmann as doctor consider Stahl's animism so important, it is because its discoveries question the fundamental principles of medicine.