Acoustic guitar refers to how the sound is produced. Twelve thousand years ago, there was no electricity, no amplifiers, so there would be no electric guitar.
Prior to the invention of the electric guitar, people played “guitar”. That is why someone like Robert Johnson is a guitarist, not an acoustic guitarist.
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I think that we definitely should have acoustic guitar as the top of the tree (after ‘guitar’). Classical, which are primarily acoustic guitars would then be a sub-category. They are acoustic guitars first. Then their specifics is what makes them classical guitars.