The more you think about what music actually is, the less obvious the answer becomes.
In different writings, John Cage made a distinction between structure (“the division of the whole into parts”) and form (“the expressive content, the morphology of the continuity”). These being distinct again from method (“the note-to-note procedure”) and materials (“the sounds and silences of the composition”.
I’ve been listening to two solo viola recordings by Jessica Pavone: Silent Spills, In the Action. In one composition, pizz chords effluviate into plumes of sound, little clouds. In Cage’s Dream, a strict textural limitation, a single line, expands into sweeps of sound at careful moments.
Here are two reasons to use notation: (1) complexity of texture or technique; (2) complexity of form/structure. If you want to say something specific in either of those ways, you might use notation. If what you want to say is simple in both of those ways, you might be better off teaching the music by rote.
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