The Theme of Opus 40: Function harmonic coherence and sequential organisation. The Theme of Carl Nielsens opus 40, Theme and Variations is well-known for its change of tonality from b-minor over f-minor ending in g-minor within a course of only 16 bars. Obviously this raises the question of "directed tonality" or "paired tonality". Being a theme of a group of variations its harmonic progression is meant to repeat itself over and over again. In this view notions of directional tonality and tonal ambiguity might most of all lead to a feeling of dizzyness. The interesting question is to my therefore, how come this theme works. How does Nielsen within a seemingly functional harmonic pattern manage to touch upon such a variety of keys in such a short pattern? How can these relations be described? Does Nielsen employ other structuring elements besides harmonic coherence? It will turn out that the harmonic progressions can be understood through theories presented by Jan Maegaard in his article Harmonisk analyse af det 19 årh.s musik, Musik og forskning 15, 1989-90, along with Neo-Riemeann transformation theory. Along with this harmonic ordering runs a sequential structuring, as the chord patterns turn out to elaborate well known basic sequences, which in the German-Scandinavian theoretical tradition goes by the names "Rosalie" and "Inganno-sequence". As such sequence-models often function as referential basic models – like Meyerian “sound terms” - forming the backbone of Nielsen’s music, I shall argue for operating with a limited number of named basic sequential patterns rather than thinking of such patterns in terms of linear interval progressions or transposition operations. And besides all this, the Theme of Opus 40 is a perfect realization of Nielsen’s famous claim: "We need to get away from the keys and yet still work with diatonic conviction".