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Extending the Major and Minor Triads by a Seventh
Major 7th Chords
Three note chords can be extended by a fourth tone to create more interesting
harmonies. The most common way to extend a three note chord is with the inclusion
of a tone that is a minor or major third above the fifth (or third chord tone).
This tone is often termed a flat seventh (b7) in the case of an added minor
third, or a major 7th in the case of an added major third. For further clarification,
consider the plain old C major chord. The C major chord in the key of C is
considered to be the I (one) chord in that key and it is created by combining
every other note in the key of C starting with the C and ending with G. C is,
therefore, spelled C-E-G. (Recall that the notes in the key of C are C, D,
E, F, G, A, and B). When we add the note B to this formula we end up
with the spelling C-E-G-B (a Cmaj7 chord). This chord is a Cmaj7 chord because the B
is a major third, or two whole steps, above the G (if this information confuses you,
please review the concepts presented in Music Theory 101).
Minor 7th Chords
Minor 7th chords are constructed from a minor triad by adding a flat 7 (b7) interval
to that triad. For this example we'll stay in the key of C (cause it's easier that
way) and use a chord built from the second note in that key, D. If we start building
a triad in the key of C starting with the note D we end up with a minor chord spelled
D-F-A (D, skip E, keep F, skip G, keep A). We call it a minor chord because it consists
of a minor third interval plus a major third interval (one and a half steps plus
two whole steps). To arrive at the proper 7th tone we take our
basic triad, the D-F-A, and extend the triad a third above A. Doing this creates a
D minor 7 chord (Dm7) spelled D-F-A-C. Please notice that the C note is a minor third
above the A (one and a half steps); therefore, the C is considered to be a flat seventh
above the D root.
Dominant 7th Chords
Constructing a chord from the fifth note in any major key will result in the creation
of a major chord. For example, the G major chord in the key of C is spelled G-B-D
(G, skip A, B, skip C, D). Unlike the major 7th chord
which results when we tack a seventh to the C-E-G triad, the G-B-D triad becomes a
dominant 7th chord when it is extended by the addition of the note F. This is
due to the fact that the F is a minor third above the G and is, therefore, a flat
seventh above the G. You can always verify this by examining the relationship of the
F to the D (it is a minor third interval above the D, or an interval of one and a half
steps above the D). The G dominant 7 chord is most commonly referred to as the G7 chord
and its spelling is G-B-D-F. Only the chord constructed from the fifth degree of a
major scale behaves in this way. A chord built from the 1st degree of the scale will
result in a major seventh chord as will a chord built from the 4th degree of a major
scale (in the key of C, that is the F). Therefore, the C note in the key of C (the
first degree of that scale) and the F note in the key of C (the fourth degree of that
scale) will result in major seventh chords when their triads are extended by a fourth note
-- C-E-G-B and F-A-C-E (where B is a major third up from the G, and the E is a major third up from the C).
Practice Tip
Practice the concepts presented on this page by applying them to other chords in the
key of C. Extend the Em and Am chords by a seventh, write out the spellings, find
all instances of the notes used to construct them on the neck of your guitar, and
then create your own fingerings. Be sure to do the same in using the chords F major
and G major. If you feel extremely ambitious, do this in all keys.
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