A point about which I've always been curious: Are the "quarter tone" modes really all that different from what we are accustomed to? I've tried to ask several musicians who played Middle Eastern music, and most were not theoretically inclined. But one street musician explained that the music he played, basically Arabic, was in the harmonic minor with one or two notes either always or sometimes sharped or flatted by a quarter tone. That would be on the order of pulling a guitar string to produce a "blue note." Or comparable to "bending" sustained notes in Klezmer music, which appears to be influenced by Middle Eastern forms. It doesn't seem to mean that a genuinely different scale with different intervals is involved.
Can it be that that is all there is to the difference, or is there really a completely different theory? And if it is completely different, can anyone actually explain the difference?