Are you a bit confused by the different types of seventh chords ? If so, understanding dominant chords will answer many of the questions that you may have. This installment of my music theory for guitar series focuses on how and why dominant seventh chords function the way they do, and how to use dominant chords effectively to add interest and creativity to your compositions.
Just to review, remember that dominant seventh chords are built by combining the first, third, fifth and flatted seventh degrees of the major scale. They occur naturally only on the fifth scale degree when harmonizing major and harmonic minor scales. Major and minor sevenths occur on multiple scale degrees and are considered as consonant, pleasant sounding chords, and they don’t exhibit a strong tendency to be followed by a particular chord in the progression. Dominant chords , however, are dissonant and unstable and they demand resolution to a consonant chord built on the tonic (root or keynote) of the key.
So, why do all dominant chords, including extended and altered variations, have a unique sound? The answer is a tritone , which is simply a diminished fifth or an augmented fourth interval. In each of these intervals, the distance between the notes is three whole tones – hence, the term tritone. Using the formula for building dominant seventh chords (T, M3, P5, m7), notice that the third and seventh form a diminished fifth tritone . Inverting the interval, with the seventh on the bottom, results in an augmented fourth tritone . And, tritone resolution is the basis for understanding dominant chord resolution . ALL dominant chords contain a tritone !
Let’s use the key of C major as an example. The staff notation, below, shows how the tritone interval contained in the V7 chord wants to move to a consonant interval contained in the I (one) chord of the key. When the G7 chord is in root position, the B and F, the tritone, want to move inward to C and E, a major third interval. If the G7 uses a different inversion, the F and B, still a tritone, want to move outward to an E and C, a minor sixth interval. Regardless of inversions and how the notes actually move, the V7 to I resolution is the strongest sound in music.
If you have a keyboard, play several V7 to I progressions in different keys. Understanding dominant chords is a lot easier if you can more easily see and hear how the dominant chords “should” resolve. But, since this is a guitar lesson, I’ve included moveable chord form diagrams, below, that show the tritones and how they should ideally resolve. Since facility of finger placement is always an important consideration, the overall sound of the chord movement is the most important thing. It really doesn’t matter which chord forms you play – a G7 chord sounds like it should be followed by a C chord. Well, almost . . . it also sounds like it could go to a C minor chord, too. And it can.
As you know, the harmonic minor scale form raises the seventh degree of the natural minor by a half step so it functions like the familiar leading tone in the parallel major key (e.g., C minor and C major). Altering the Bb in a C minor scale to a B now changes the chord built on the fifth degree from a minor seventh to a dominant seventh chord . The resultant G7 chord wants to resolve to a C minor (the i chord). Although I haven’t included staff notation or chord diagrams for V7 to i resolutions, try both major and minor.
In the following diagrams, the tritones are light blue and the resolved intervals are light purple. Remember that the fret number indicates the fret in which your first finger must be placed.