Thirteenth - Dominant Thirteenth

Most commonly 13th chords serve a dominant function (V13), whether they have the exact intervals of a dominant thirteenth or not. Typically, a dominant chord anticipating a major resolution will feature a natural 13, while a dominant chord anticipating a minor resolution will feature a flat 13. Since thirteenth chords contain more than four notes, in four-voice writing the root, third, seventh, and thirteenth are most often included, excluding the fifth, ninth, and eleventh Play. The third indicates the quality of the chord as major or minor, the seventh is important for the quality as a dominant chord, while the thirteenth is necessary in a thirteenth chord.

In modern pop/jazz harmony, after the dominant thirteenth, a thirteenth chord (usually notated as X13, e.g. C13) contains an implied flatted seventh interval. Thus, a C13 consists of C E G B♭ and A. The underlying harmony during a thirteenth chord is usually Mixolydian or Lydian dominant (see chord-scale system). A thirteenth chord does not imply the quality of the ninth or eleventh scale degrees. In general, what gives a thirteenth chord its characteristic sound is the dissonance between the flat seventh and the thirteenth, a major seventh.

In the common practice period the "most common" pitches present in V13 chord are the root, 3rd, 7th, and 13th; with the 5th, 9th, and 11th "typically omitted". The 13th is most often in the soprano, or highest voice, and usually resolves down by a 3rd to the tonic I or i. If the V13 is followed by a I9 the 13th may resolve to the 9th.