<P> The above passage starts in F major and modulates to B flat major and then, via the chord of G to C major . Sometimes sequential passages combine more than one of the above characteristics . In the third and fourth bars of the "Air" from J.S. Bach's Orchestral Suite No. 3 in D major, the violin part forms a tonal sequence with the notes modified to fit the harmony, while the intervals in the bass line are unchanged, creating a real sequence . The whole passage also forms a modulating sequence, starting in D major and moving through E minor at the start of the fourth bar: </P> <P> A sequence can be described according to its direction (ascending or descending in pitch) and its adherence to the diatonic scale--that is, the sequence is diatonic if the pitches remain within the scale, or chromatic (or non-diatonic) if pitches outside of the diatonic scale are used and especially if all pitches are shifted by exactly the same interval (i.e., they are transposed). The non-diatonic sequence tends to modulate to a new tonality or to cause temporarily tonicisation . </P> <P> At least two instances of a sequential pattern--including the original statement--are required to identify a sequence, and the pattern should be based on several melody notes or at least two successive harmonies (chords). Although stereotypically associated with Baroque music, and especially the music of Antonio Vivaldi, this device is widespread throughout Western music history . </P> <P> The device of sequence epitomises both the goal - directed and the hierarchical nature of common - practice tonality . It is particularly prevalent in passages involving extension or elaboration; indeed, because of its inherently directed nature, it was (and still is) often pulled from the shelf by the less imaginative tonal composer as the stock response to a need for transitional or developmental activity . Whether dull or masterly, however, the emphasis is on the underlying process rather than the material itself . </P>

Sequence occurs when pattern of notes is repeated