One of the most interesting things about music is how the clearly psychological enjoyment of music correlates with certain types of acoustic phenomena. While is would be a mistake to say that good music correlates perfectly with harmonies that reflect simple mathematical relationships, there is a clear relation between simple mathematical relationships in the frequency of sound waves, and stereotypically enjoyable music. While dissonance is an increasing characteristic of music over the last few hundred years, this is not just any dissonance. Instead, it would be better to say that it's a very tangentially developed version of order. The blue notes heard in jazz or blues music (among others) are not dissonant for the sake of disorder. Rather, their dissonance creates a tension in the underlying order that, when developed and resolved skillfully by the musician, is a celebration of that order; a gesture that attempts to cleverly, passionately, triumphantly, ...---reaffirm that order.

The appreciation of more profound dissonance as it relates to order is a clearly more developmentally complex state than the appreciation of moderate, or minimal dissonance. For example, appreciation of elevator music is more simple than appreciation of modern jazz. Elevator music is so simple as to be boring. Modern jazz may be complex enough to sound completely disordered.

Learning a musical instrument is an interesting application of this type of thinking. What are the different ways that the development of the appreciation of music--in particular the harmonic aspects of music--can relate to the development of the ability to play an instrument. One possibility is that there are two alternative developmental relationships between harmonic appreciation and instrument ability. One is that the musician learns the instrument while still at a primitive level of harmonic appreciation, and the development of harmonic appreciation is scaffolded by the instrument as a psychological structure. The other is that advanced harmonic appreciation develops far in advance of musical talent. In this case, an awareness of how certain notes relate to the harmonic order of the song is embodied not by knowledge of the instrument, but instead by some internalized spatial schema that does not relate to the instrument. The latter type of musician would be able understand how complex harmonies relate to a song without being able to express this flexibly, or with any depth, with the instrument. The difference between these two possibilities is equivalent to the difference between a person who knows something in a way that is difficult for them to communicate (which doesn't mean that they don't know it), and a person who can easily communicate the same knowledge. In this example, language command functions the same way that command of the musical instrument does.