 Mehrtens (1990a, 1990b, 1996) describes, in terms of styles, the conflict in mathematics between “formalists” and “logicists” on the one hand and “intuitionists” on the other hand as a battle between two conceptions of mathematics (see also Gray 2008 for a critical take on of Mehrtens’s approach while emphasizing the “modernist” transformation of mathematics). Hilbert and Poincaré are used as paradigms for the sources of the opposition that later led to the Hilbert-Brouwer foundational debate in the 1920s (on the history of the Brouwer-Hilbert debate see Mancosu 1998). Mehrtens also points out that this opposition did not necessarily run along national lines as, for instance, Klein could be seen as close to Poincaré. Indeed, a certain internationalism in mathematics was dominant at the end of the nineteenth century and the early part of the twentieth century. However, WWI was to change the situation and gave rise to strong nationalistic conflicts. A central player in ‘nationalizing’ the opposition was Pierre Duhem who opposed the esprit de finesse of the French to the esprit de géométrie of the Germans: