There are twelve tones because the pitch between them is the smallest one that our ear can differentiate as two distinct tones. Is the pitch smaller, you hear only beats.
In short: no you're factually wrong. Human ear can discern smaller pitch changes and there actually music composed on smaller subdivisions than 12
For instance https://en.wikipedia.org/wiki/19_equal_temperament
You can check done pieces on YouTube.
Yes it sounds unusual. Yes it sounds strange. But thats just because you've been conditioned to listen 12 tet all your life.
But saying 12 notes because we can't perceive smaller changes is, again, wrong and there's actual counterexamples of music done with smaller changes
“Ragas are precise melody forms. A raga is not a mere scale nor is it a mode. Each Raga has it’s own ascending and descending movement. And those subtle touches and uses of micro tones and stresses on particular notes like this…”
Microtones are less than the difference between two adjacent pitches in western scales and are discernable, even to people like me who have a hard time telling adjacent pitches apart.
For example, lots of the notes in the vocal of the Beatles `Come Together' are clearly (often very) flat — wonderfully so, subversively so, even, in our pitch-corrected age!
A very small gap gives a subtle chorus effect, a little wider takes one into honky-tonk piano territory, and wider still perhaps more like a bell, but still sounding like one note.
But, as you say this doesn't negate the audibility of microtonal inflections in a melodic line.
However, pitch steps smaller that those of 12tet can still provide new chords. For example, in 24tet the triad with a third half-way between minor and major is a distinct and interesting sound. But yes, in 24tet two consecutive pitches sounded together sounds more like a single note with an interesting timbre.
There are systems that have more than 12 notes.
Plenty of instruments hit these "microtones". E.g. string instruments with frets can bend strings, and string instruments without frets can just play those notes.
Genres of music like the blues frequently utilize these microtones.
12TET is just the custom in western music, but we can absolutely discern smaller intervals.
I'm sure at some point those tones will converge into a single note to human ears, but the fact that a 53-note keyboard exists shows that people can absolutely hear smaller divisions than just the 12 standard notes.
https://www.sciencedirect.com/topics/medicine-and-dentistry/...