Understanding the Function of Major Chords
The Theory and Role of Chordal Extensions in Diatonic Harmony
Apr 21, 2009
The chordal world is vast, if not infinite and accompanying instruments possess an incredible diversity of voicings and variable chord structures. Chords are based off of triads, which are three notes played together.
In jazz, triads are often embellished with other notes which are called extensions. These other notes add color to the triads and create powerful dissonance and tension which can fit specific moods in the music.
Major Chords
Most commonly, chords consist of triads. A triad is a group of three notes played together-root, third and fifth. In a C major chord, the triad consists of the notes: C E G. The C (root) is in the bass, E (third) is a major third above C and G (fifth) is a perfect fifth above C. Note that G is also a minor third above E. The major chord is unmistakably "happy" or "bright," but often played with other notes added to the triad.
Extensions
The major seventh (M7) is a very common chord seen on many charts. It is designated by a small triangle next to the chord. It is a major triad with a major seventh added above the bass. For example: C E G B. Note that the interval between B and C is a half step. Depending on the voicing of the chord, this minor second interval adds a variable amount of dissonance.
Other extensions like sixths, ninths and sharp elevenths are also common. C6 is comprised of the notes: C E G A. Note that this actually transforms the chord into a minor 7th chord. CM9 is a major seventh chord with an added ninth. A ninth is the same interval as a second. This chord can be played with all five notes, but more commonly the fifth is omitted and the spelling is: C E B D.
Sharp Eleventh chords are written either #11 or b5. In the case of M7, the #11 convention is used. These chords contain a tritone and therefore are quite dissonant. CM7#11 is spelled: C E F# B. Note the tritone interval between C and F#. Also, as written, the interval C to F# is an augmented 4th, it is actually a diminished 5th (C to Gb) and the chord retains its root, third, fifth, seventh requirements.
Major Chords in the Major Scale
Chords are based off of the diatonic scale. In the major diatonic scale there are three naturally ocurring major triads. They occur in positions I, IV and V. Look at the notes of the C major scale. There are eight notes with no sharps or flats in one octave and different chords can be built on each step, all of which still retain the basic root, third, fifth and seventh properties.
C D E F G A B C
On step I, C major occurs: C E G (B) On step IV, F major ocurs: F A C (E). On step V, G major occurs: G B D (F). Note that step V in the major diatonic scale is a dominant chord and not a major seventh when the seventh (F) is added. It is important to play these chords on an actual instrument to see how they are composed and how they function.
A major third has 4 half steps between root and third and a minor third has only three. This can easiliy be visualized on a piano or a guitar. The most basic way to visualize the spacing between the notes in a chord is to count the half steps between each note:
C to E: 4 half-steps. E to G: 3 half-steps. G to B: 4 half-steps.
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