Function is a much harder concept to define than Art, for me. I am not very happy with the term, but I will do my best do clearify what I put into it. Carl Dahlhaus (1970) calls it Genre-music, which in a way perhaps is a better term, but I will stick with Function, since that is the term I have got used to.
Functional music is music that has an ‘outer’ purpose. It may be dancing, it may be a ceremony (like a wedding or a funeral), it may be as a means for friends to hang out together. All this also implies that functional music is music where everyone is somehow participating, there is no real division between performer/creator and audience, everyone is necessary and the one would not exist without the other. Hence functional music depends on (the approval of) the collevtive and doesn’t really give space for the individuality.
Functional music is also music that follows clear and straight lines that are defined by this purpose: If I’m playing for dancing it is the danceability of the music which defines its value; If I’m playing togethere with a group of people it is the musics ability to fit into the taste, style and technical ability of the group that defines its value. This creates a very comfortable space to move within. As long as you’re keeping inside these frames there is a great deal of freedom and it is easy to know what is good and what is not. Quality in this context is about reproducing tradition and convention, fulfilling the requirements of the genre.