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Music theory was Al-Farabi's area of expertise in music. He was a renowned philosopher and scientist who made significant contributions to the field of music theory. His writings on music, such as the "Kitab al-Musiqa al-Kabir" (Grand Book of Music), explored the mathematical and philosophical foundations of music, including scales, intervals, and rhythms. Al-Farabi's work had a profound influence on subsequent music theory in both the East and the West.