 So far, Malebranche has not said anything with which Descartes would disagree: the fact that ideas have properties and resist our thought demonstrates their reality. But Descartes also speaks of ideas as ‘immutable and eternal.’ Malebranche concurs with this as well, and adds that they are ‘necessary,’ ‘universal,’ and ‘infinite’. The idea of extension, for example, is ‘necessary, eternal, immutable, and common to all minds….’ (ibid., OC 12:42; JS:14) To say that ideas are ‘necessary’ just means that ‘it is impossible that they should not be as they are,’ and this is something that Malebranche thinks is discoverable in thought (Elucidation 10, OC 3:130; LO 614). Ideas are infinite in the sense that they are ‘inexhaustible.’ One can discover in the idea of extension, for example, ‘infinite numbers of intelligible triangles, tetragons, pentagons, and other such figures,’ as well as an infinite number of truths that can be demonstrated of them (ibid.). The ideas of extension and the various geometrical figures are also immutable (or unchanging) and eternal in the sense that they did not come into being, and will not go out of being. And although cultural norms and tastes may vary among cultures, races, and periods, the truths of mathematics are universal and common to all intelligences in the sense that all minds will, upon reflection, discover the same ones. Such truths are not the product of convention but are intellectual givens that impose themselves on our thought.