Extensions

As we have seen, chords are made up of notes from the major scale then modified into the different chord types (major, minor and dominant). To be specific, chords use every other note from the scale. A chord is a scale, arranged in thirds. Most often, the 7th. is the top note of a chord because, that completes the octave and we run out of notes. However, if we continue stacking notes in thirds into the next octave, eventually, all seven notes of the scale are included in the chord. This is the idea behind extensions. The notes in the chord above the seventh are the extensions.

Pictured above, is a C major scale, written in two octaves. The notes are numbered and the chord tones have been circled. Rather than count the second octave from one, when dealing with extensions, the second octave is counted from eight. Eight and one are the same note (one octave apart), nine and two are the same and so on. The "extensions are the 9, 11 and 13. There is no need to deal with 8, 10, 12 or 14 because they are repeats of 1, 3, 5 and 7; the notes which already make up the chord. To the right of the two octave scale, is a chord stack made up of 1, 3, 5, 7, 9, 11 and 13. This is the Cmaj7 chord with all the possible extensions added (9, 11 and 13).

Viewed this way it could be said that a chord and scale are the same thing since both are made up of the same notes. When adding extensions to a chord, it is not necessary to use all of the possible extensions. Which ones to include is a matter of taste or is expressed in the chord notation. For example: Cmaj9 is just a C major chord with the ninth (D) added. In this case, the 7th. is optional but is likely to be included. All of the extensions work this way. Their usage is simply the chord + whatever extensions are called for in the chord notation.

Adding extensions to a chord (while changing it,s timbre) does not change it,s function so, in most instances, extended versions of a chord may be used interchangeably with the regular chord voicing. The construction of extended chords is listed in the lesson voicing chords along with some typical ways they are played on the bass.