When I first began to investigate the music and musical practices in the Sultanate of Oman, my attention was drawn to the use of different names for the same instrument. It became soon apparent that this was not a philological problem, but rather a question of the instrument's function in a given context. For example, a cylindrical, double-headed drum is called kāsir only when it appears in conjunction with a larger, lower sounding cylindrical double-headed drum, a ra&māni. A drum is called ra&māni only when it fulfills the function of providing the rhythmical framework. Then, the kāsir takes on the function of “filling-in” or embellishing. However, the same kāsir can function as a ra&māni. In this case, it appears in combination with an even smaller kāsir. Thus, function correlates with relative size, and determines the nomenclature.