Study of the twelve dastgāhs has shown that the radif of each dastgāh includes pieces that are exclusive to it, and also some that are taken from the radif of other dastgāhs. There is still another group of pieces that are performed, or can be performed, in all of the dastgāhs. The pieces in this group have relatively stable melodic and rhythmic structures and are not subject to extensive change through improvisation. More important is the fact that they have no modal stability. They adopt the mode of the dastgāh in which they are placed, or even the mode of gušes which have preceded them. As such, while the melodic and the rhythmic identities of these pieces are preserved, their modes change according to where they are placed. The word tekke (small or short piece) will be used here to identify this genre of guše. Writers on Persian music have generally failed to recognise that, due to their instability and adaptability, these pieces must necessarily be placed in a separate category. At times they are identified simply as zarbi or rhythmic pieces.

There are two types of tekke: those that have a more or less clear and stable metric structure and are exclusively instrumental (we shall call this group rhythmic tekkes); and those that do not have a stable metric basis and can be performed vocally as well as on instruments (we shall call this group non-rhythmic tekkes).