Duhem's great contribution to the study of the history of medieval science is indisputable. His book remains an excellent source of information concerning the ideas of the epoch's thinkers about the foundations of the universe. Ariew's painstaking translation of a considerable portion of Duhem's ten-volume work deserves the deep gratitude of all those interested in medieval science. Le Systéme du monde regains its actuality. Nevertheless, to write now about a book produced by this great scholar at the beginning of the century is not an easy undertaking, and involves some risk. Too many changes have taken place in the principles of studying the history of science during the seventy-odd years since the book was written, and some notions that seemed then to be perfectly clear are not so simple and indisputable now. With profound respect for this feat of scholarship, I should like to make some observations in connection with the recent English publication of Duhem's book.