We learn to read music as if tone were something defined, discrete, spellable. Having learned that visual skill it gets harder and harder to trust that what we actually hear when we process tones has a broader reference.
Having learned the rudiments of music many proceed on to theory classes. Here we are taught to identify complex sets of tones by giving them chord names and then to specify their functions with a system of Roman numerals. Those Roman numerals are based on an assumption of tonal hierarchy which may or may not apply, depending on the instrument producing the sounds and sometimes on the skill with which a composer unhitches the chords from their traditional hierarchical stability.
I think of much of the piano music of Debussy and Ravel: It belongs to a white key / black key world, not simply to a world of specified tonality. I think also of Schubert's great B-flat Piano Trio where he goes to considerable pains to produce a tonal system in which the minor triad on the 2nd scale degree is entirely unrelated to the tonic triad.
Burdened down with an inflexible system it becomes harder to hear and to trust that hearing is the key to understanding music.
