The overlapping nature of these classes may be very confusing to our spaceman until he realizes that these labels are based upon totally different criteria. A similar situation exists with Indian percussion. Function , structure and bol are three independent criteria used to define our compositional forms. One typically finds one or two criteria used for a definition but rarely one will find all three. Therefore, it is common to find the same composition called different things on different occasions by different musicians.
Function is the criterion that concerns how and when a musician uses a composition.
There are some pieces which are reserved for specific styles such as light, filmi , classical, folk or dance music. Function may be thought of as a gestalt of artistic, traditional and stylistic factors. Two forms may be said to be functionally identical if they may be interchanged. Therefore, at the level of function the two are identical, though they may be differentiated at another level. Structure is the criterion based upon the anatomy of the composition.