Diatonic sequences repeat musical segments and are transposed in a regular pattern within a key.

Chromaticized diatonic sequences include can include chromatic embellishments or chromatic chords, such as applied (secondary) dominants. These sequences avoid strict transposition of both interval size and quality.

Chromatic sequences differ from diatonic sequences in that both the size and quality of the interval of transposition is maintained throughout the sequence. Diatonic sequences preserve the interval size, but not the quality, to ensure that they stay within a single key.

Remember, with all sequences, the voice leading must be consistent within every voice. Chord voicings should match between all corresponding components.

Descending-Fifths Sequence

Consider the following two-chord sequence (Example 1), often referred to as the "descending-fifths sequence."

Example 1. A diatonic descending-fifths sequence.

The sequence model, a root progression by descending fifth, is transposed down by second in each subsequent copy of the model. Because the sequence uses chords entirely from the key of G major, the root progressions don't match exactly throughout the sequence. For example, the root progression between the IV and viio chords is an augmented fourth, whereas the root progressions between every other pair of chords is either a perfect fifth or perfect fourth. We "cheat" in the sequence in this way in order to keep the music within a single key. If the interval between successive chord roots was consistently a perfect fifth/fourth, the root progression would be as follows: G–C–F–B♭–E♭–A♭–D♭… and so on. The sequence would rather quickly bring the music outside of the key of G major, and into new chromatic territory. It would become a chromatic sequence.

Chromatic sequences differ from their diatonic counterparts in a few important ways:

The chords that initiate the sequence model and each successive copy contain altered scale degrees.

The chords within the pattern are of the same quality and type as those within each successive copy of that pattern.

The sequences derive from those that divide the octave equally.

Importantly, chromatic sequences are not merely sequences that contain chromatic pitches. Example 2 shows the same descending-fifths sequence, this time with alternating secondary dominant chords. While the sequence contains chromatic chords (the secondary dominants), it is not a truly chromatic sequence because the overall trajectory of the sequence is still one that traverses the scale steps of a single key. Notice that the progression of chord roots on successive downbeats still matches the purely diatonic sequence shown in Example 1: G–F♯–E–D.

Example 2. A diatonic descending-fifths sequence with alternating secondary dominant-seventh chords.

Conversely, we can create a truly chromatic sequence if we ensure that the progression of chord roots maintains a consistent pattern of intervals throughout the sequence. An easy way to do this is to make the second chord of the sequence model into a dominant-seventh chord that can be applied to the first chord of the subsequent copy of the model. In Example 3, the second chord of the model is now F7 instead of a diatonic IV chord. We interpret this as V7 of the chord that follows, which is, in turn, another dominant-seventh chord.

Example 3. A chromatic descending-fifths sequence with interlocking secondary dominant-seventh chords.

The voice leading in the above sequence requires some attention. Because every chord is interpreted as a dominant-seventh of the chord that follows, it is not possible to resolve both the leading tone and the chordal seventh as normal. As is the case whenever you connect seventh chords with roots a fifth apart, the voice leading requires an elided resolution. Instead of the chord you expect to hear following a dominant-seventh chord, you get a dominant-seventh chord with the same chord root. For example, we expect to hear either a C or Cm chord following a G7 chord. An elided resolution would result in a C7 chord in place of the expected chord. An example of an elided resolution is shown in Example 4. The example shows the expected C resolution in parentheses. The elided resolution essentially "elides" the chord we expect with the following chord, C7. In a sense, we mentally skip over the expected chord to get to the next dominant-seventh chord. An important result of the elision is that the leading tone of the first dominant-seventh chord, B, resolves down by half step to become the new chordal seventh. Likewise, when the chordal seventh in the first dominant-seventh chord, F, resolves down by half step, it becomes the new leading tone. This leading tone/chordal seventh exchange is essential for proper voice leading in chord progressions that use interlocking seventh chords, such as the sequence above. Furthermore, this kind of voice leading is integral to the study of jazz harmony, as you will find in other parts of this textbook.

Example 4. An elided resolution of a dominant-seventh chord.

Returning to Example 3, notice that the progression of chord roots on each successive strong beat divides the octave equally into major seconds. This results in a sense of tonal ambiguity, making the Roman numeral analysis of these chords tenuous, at best. In particular, the chords identified with asterisks in the example are only labeled as such for consistency. In many cases, when analyzing highly chromatic music, it is often quite difficult to assign Roman numerals to chords; this tonal ambiguity is part of the aesthetic of this kind of music. In cases like this, it is often convenient to also analyze the music using lead-sheet symbols. These have been included in the examples in this chapter.

Ascending 5–6 Sequence

Example 5. A diatonic ascending 5–6 sequence.

Example 6. A chromaticized diatonic ascending 5–6 sequence, featuring secondary dominant chords.

The above examples present the diatonic ascending 5–6 sequence