rly concerned with the question of the criteria for choosing hypotheses, combating arbitrariness. A first case of arbitrariness is the one resulting from the conventional choice of the definitions that allow the measurement: In order to represent the same notion, one can in general make use of a multitude of extremely different magnitudes (...) the simple change of the definitions would already lead to changing the hypotheses [which would correspond to translate] the same hypothesis by means of different symbols, and these two statements of the same hypothesis in two different systems of symbols do not constitute any more two different hypotheses than the statements of the same proposition in French, Latin and Greek constitute three different propositions. (Duhem 1892a, 152) This adjustment between definitions and hypotheses reminds one of Poincaré's reflections: Poincaré speaks of the intertranslability of metric geometries and the fact that the choice of a physical geometry (which makes it possible to measure lengths and angles) implies a set of rules of coordination with empirical definitions; Duhem notes that the conventional choice of definitions (which allow measurement) implies adjustments in the hypotheses, but that these adjustments are related to each other as translations in different languages of the same idea. Also their discussions on the concept of temperature (their common sources being 15 On the conventional character of the equality of temperatures in (Poincaré 1892a) see Darrigol (2003, 563). Darrigol shows that Helmholtz inspired the conceptions of Poincaré and Duhem on measurement; Duhem is individualized by his ideal of a physics of qualities, a neo-Aristotelian conception according to which qualities remain irreducible to quantity – "a property identified as a quality had to remain a quality for ever" (Darrigol 2003, 568), thematic preference (in the sense of Holton) to which Duhem remains faithful throughout his career. On the history of the concept of temperature see also (Chang 200