The “Essai sur la notion de théo­rie phy­sique” by Pierre Duhem has been contes­ted and rejec­ted both by those who see it as an apo­lo­ge­tic for the Gali­leo affair, but also by those who refuse to see in this essay an his­to­ri­cal argu­ment in favour of Duhem’s phe­no­me­na­lism. Howe­ver it would appear that both groups of cri­tics have not taken suf­fi­cient notice of this mono­graph in Duhem’s works. Without wan­ting to unde­res­ti­mate the apolo­getic inten­tion of Duhem’s essay, this article argues that the author desi­red to esta­blish his­to­ri­cal­ly the vali­di­ty of a pheno­menalist posi­tion. This is a posi­tion which the author consi­de­red to have been alrea­dy phi­lo­so­phi­cal­ly esta­bli­shed in “La Théo­rie phy­sique”. These are the same his­to­ri­cal argu­ments which were later to be deve­lo­ped in “Le sys­tème du monde”. It would appear that the “Essai” can be inte­gra­ted seam­less­ly into the entire cor­pus of Duhem’s work, deve­lo­ping pre­vious argu­ments and esta­bli­shing themes which were deve­lo­ped in later works.