Chord Functions


If you've looked at the chord naming page, you'll have come to the realization that there are a large number of possible chords. Now the question is, how to decide which chords to choose.

The answer to this really depends on what kind of music you want to play. I'm going to assume you are playing jazz standards, which have a definite sense of key area at least most of the time. There are certain styles of jazz in which the key area is supposed to remain vague and undefined. In that case, any chord can move to any other chord. But if there is a sense of key area, we can discuss some typical structures and uses.


For this purpose, we can classify chords into basic types depending on the lower degrees of the chord, and ignoring for the moment the higher degrees. We find the following common types:

For a more detailed discussion of these concepts, read William Russo's Composing for the Jazz Orchestra (University of Chicago Press, 1973).


maj 7

The major 7th chord can be used as a tonic chord, built on the root of the current key area. It may also be a subdominant chord, built on a root a fourth higher than the tonic, in which case it would have a +11. The subdominant is a point of temporary repose, which tends to want to go back to the tonic.

m maj7

The minor major 7th chord typically is the tonic, or possibly the subdominant chord in a minor key area. As a subdominant, it might well have a +11.

7

The 7th chord (with no altered degrees) usually wants to resolve to a chord with a root a fourth higher. This could be a tonic chord in a major key, or possibly another 7th chord, because you often have a chain of several 7th chords all a fourth higher (or a fifth lower) than the previous one. In general, though, it would go to a chord with a major 3rd. Note this is the same note as 13 of the seventh chord. When resolving to a minor chord a fourth higher, you would usually lower the 13 to a -13; it is thus the same note as the 3rd of the minor chord coming up. If you are playing blues, however, the 7th chord has no tendency to resolve and can be used as a stable tonic chord.

altered 7

An altered seventh chord has had some or all of its degrees altered, such as -13 -9 -5 (in increasing order of likelihood). This type of seventh chord will resolve to a minor tonic a fourth higher (note that the -13 is the same note as the minor 3rd degree of the tonic chord). It will also resolve to a major tonic. The more degrees that are altered, the greater is the urge to resolve. After several degrees are altered, the phenomenon of tritone substitution is encountered. The chord is becoming enharmonically equivalent to a seventh chord a tritone away, that is, a semitone above the tonic. The enharmonic equivalent usually tends toward a 7+11 chord. (The +11 is the same note as the root of the original altered 7th chord.)

m7

The minor 7th chord can be generated at three different positions on a major scale. Therefore the minor 7th chord would naturally fulfill the harmonic functions ii, iii and vi. (The degrees 9 and 13 would be altered as appropriate.) These all have a tendency to resolve a fourth higher. Particularly, a ii m7 would tend to resolve to V7 and then to I maj7, .i.e., ii V I in a major key.

m7-5

Russo calls this a "leading tone seventh type chord". The most common m7-5 is the one generated in the Locrian mode, i.e., m7-5-9-13. It's most common function is a ii chord in a ii V i progression in a minor key.

dim

The diminished chord is typically used as a sort of ambiguous passing chord between two other chords that have no particular tendency to be connected. It is also used to harmonize chromatic root movement.

aug

The augmented chord is rarely used. Usually the term is used in error for an altered 7th chord with a -13.



Note that when I point out that a certain chord has a tendency to do something, that doesn't mean it does it all the time. Music would be boring if it always did what was expected. The way you add interest is by doing the unexpected. On the other hand, if you always do the unexpected, you will lose all sense of key area; this may be the desired effect!



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