 In La Géométrie, the relation between straight and curves lines was considered inexact because, as Descartes put it, “the ratios between straight and curved lines are not known, and I believe cannot be discovered by human minds” (G, 91). That Descartes later admits that he can clearly and distinctly conceive such a relation suggests, according to Mancosu, that the stated criteria for geometrical curves presented in La Géométrie reveals only part of Descartes’ mathematical agenda. A more complete portrait must, Mancosu argues, take into account Descartes’ commitment to the impossibility of squaring the circle (see Descartes’ letter to Mersenne, 13 November 1629, AT 1, 70–71; translated in Mancosu 2007, 120; see also Mancosu and Arana 2010 for further evidence in support of the position of Mancosu 2007).