The melancholy thirteen-bar prefatory theme (“Mesto”) of the Sixth Quartet, which introduces each of the four movements in the work, has received much attention by writers on Bartók. Such terms as ‘motto theme’, ‘idée fixe’, ‘signature theme’, and ‘ritornello’ have usually been used to describe it, indicating that the work heralds Bartók's direction away from arch form—the structural method of his two preceding quartets—and towards cyclic form as a means of achieving overall unity. The sketches of the work, however, and the documents relating to it, suggest that the use of the prefatory theme as a cyclic link was not part of the original plan; that the work as first conceived would have shown an even more radical abandonment of the principles of thematic unification characteristic of nearly all Bartók's major works of the previous decade; and that the particular cyclic connection between the first and last movements was a structural modification based on new expressive needs which arose during the course of the composition of the work.