The Compendium is both a treatise on music and a study in methodology. In it Descartes shows himself to be a link between the musical humanists of the 16th century-he was influenced particularly by Zarlino, whom he cited-and the scientists of the 17th. The work is noteworthy as an early experiment in the application of an empirical, deductive, scientific approach to the study of sensory perception and as being among the earliest attempts to define the dual relationship between the physical and psychological phenomena in music.

Descartes divided music into three basic component parts, each of which can be isolated for study: the mathematical-physical aspect of sound, the nature of sensory perception and the ultimate effect of such perception on the individual listener. He considered the first of these to lend itself to pure scientific investigation, since it is independent of personal interpretation. He characterized the process of sensory perception as being autonomous, self-regulating and measurable. This is the realm where practical aspects of music are dealt with (e.g. rules for counterpoint) and to which the great bulk of the Compendium is devoted. To Descartes the impact of sound on a listener's emotions or ‘soul’ is a subjective, irrational element and therefore incapable of being scientifically measured. He described it as a psychological-physiological phenomenon that clearly belongs to the areas of aesthetics and metaphysics, of which he was to develop the principles later in his philosophical writings. The distinction he made in the Compendium, between sound as a physical phenomenon and sound as understood by the human conscience, permitted him to pass from a rationalist concept of aesthetics to a sensualist one in his later work. This concept was influential in the development of a philosophy for the affections in music in late 17th-century Germany, especially through his treatise Les Passions de l'âme (Amsterdam, 1649).