Augustine's treatise De musica reflects a double tradition. The first, common to classical antiquity, at least since Plato, consists in the difference between musical practice and theory, that is, between cantus and musica. Only the latter is worthy of being studied by a well-educated free person. This is the reason why the first five books of the De musica are, in fact, a treatise on meter, or more precisely, prosody, and not on music in the modern sense of the term. The second tradition is properly Christian: the more a study brings man into contact with God, the more value it has. This principle finds its justification in book VI, which is the climax of the preceding books.
In the first five books Augustine looks to demonstrate the rational structure of music as a science, then, in the sixth, he attempts to analyse the process by which the soul perceives music. He distinguishes six levels which he calls 'numbers', analogous to the 'number-rhythms' which form the structure of the scientia musica. These levels are: numeri sonantes – in the physical sound, numeri occursores – in the sense which perceives them, numeri recordabiles – in the memory, numeri progressores – in the activity which produces them, numeri sensuales – in the aesthetical judgement, and numeri iudiciales – in the rational judgement. The analysis of these numbers retraces the way by which the rational sound ascends a corporeis ad incorporea. By leaving sensible reality, the soul, - familiar with this sensible realm, but not attached to it - progresses towards intellegible reality, and from there, towards God in whom is found Perfect Beauty and Truth. [abstract, The analogy of the soul towards God in Augustine's De musica p. 128]