Comment by fifticon

I am aware you didn't specifically ask for answer, but I was not satisfied with the answers you got :-), so I'll add my two cents.. I have 3 points to make. (1) The first is about 'when does it make sense for a song to use more than 7 notes?' WHEN we do this, we will often say "this song uses a key change". Some keys have partial overlap - note-sequences they share, and ranges where they differ. One elegant way to exploit this, is to let the song meander into the common range of the two keys, and then meander OUT of that range into a different key that we used to get IN to that range. This can produce a cool surprise effect, a bit like looking at those optical illusion pictures that you can look at two ways. A similar trick can be used with rhythms that overlap, instead of frequencies that overlap.

(2) Where does the "rule" of 7 come from, ie what shapes it: As you know, notes have harmonic friends that they resonate well with. So when you are picking a 'colour palette' of notes that go well together, you will of course often pick such 'friends'. However, the more notes you already have in your picked pool, the harder it gets to add another note, that will still mesh nicely with all those previous choices. Your remaining choices will be more and more likely to clash; in particular it will be more and more likely to be "close" to one of your existing choices. And close notes clash. So, on a 12-note scale, 7 is about the optimal number of tones you can pick without them clashing too much. It is just a convention however, so some stubborn individual might come up with an 8-note scale. Once you start with 8 notes, you would be tempted to employ extra "OK I have 8 notes, but I try to avoid playing THOSE TWO back to back"-rules.

Then again, I often hear my 10-year old loudly playing .. sounds(music?) from tiktok and its ilk, and as an old geezer, I am starting to think that some of our youngsters have given up on scales altogether..

I have no idea what my third point was, at this point.