It would begin with what I consider to be music theory first principles. I think this is taught incorrectly in institutions. This causes people to fixate on the wrong things, which leads to poopy-sounding computer-generated music.
Western Music Theory is centered around one instrument. Piano you say? BZZZ! WRONG. Don't let Big Piano fool you. It *all* starts with the human singing voice.
It all begins with melody + plainsong/gregorian chant. Intervals, step-wise motion, etc. Basically, what goes into a making a good melody.
From one melodic line comes multiple melodic lines running at once. This is known as counterpoint. The challenge to solve here is how to get many monophonic sounds playing well together.
From counterpoint, the concept of harmony and harmonic structure naturally falls into place.
@mathew It's a hard one to answer definitively. The scale in Western music, as well as the intonation of those scales, evolved quite a bit over the centuries. Most of what we consider to be music theory just comes from musical trends seen in 18th century Europe, and at that point the notion of a scale was very much an established axiom. The division of the octave into 12 parts comes from the invention of Equal Temperament, which is what we still use today.
If Quora is to be trusted, this answer provides some interesting historical insights into the matter: https://www.quora.com/How-did-Western-music-%E2%80%9Csettle%E2%80%9D-on-a-12-tone-scale?share=1
@paul What I mean is, you can start from "frequency f and 2f sound good together because of how the ear works" and the concept of harmonics, and get from there to 12 approximately evenly spaced tones existing that will sound good in various combinations. Then you can discuss temperament, and subsets of the 12 to form specific keys.
Sure, that's a common way to derive it. IMO it's a bit of an oversimplification compared to how it works in practice (especially for fretless instruments).
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