 A particularly interesting theme in this sprawling treatise is the contrast between the rational structure of music and its sensuous appearance, best illustrated through Mersenne’s discussion of consonance. Having defined consonance in terms of coincidence in air vibrations, Mersenne had to explain why consonance and sensory agreeableness do not always go hand in hand. For instance, the major third is more agreeable than the fourth, although this is more consonant. Mersenne had an interesting correspondence with Descartes on the matter, in which the former manifests his wish to provide a definition of agreeableness that is as objective as that of consonance, while the latter expresses skepticism about the project, and claims that agreeableness is dependent on variation in taste, as well as in musical context (see Jorgensen 2012).