Seventh Chord Construction | Dominant Seventh Chords (3 of 5)
A Dominant seventh chord is unique in that it consists of the notes of a Major triad but with the addition of an interval of a minor seventh above the root note. This combination of a Major triad and minor seventh interval is what gives the Dominant seventh chord its defining sound.
To get a better idea, let's put together a Dominant seventh chord above the root note C.
The notes of a C Major triad are C, E and G,
and an interval of a minor seventh above the note C is the note B-flat.
By playing the notes of a C Major triad together with the note B-flat we will have constructed a C Dominant seventh chord.
In that same way, the notes of a G Major triad are G, B, and D,
and an interval of a minor seventh above the note G is the note F.
By adding F to the notes of a G Major triad we will have created a G Dominant seventh chord.
Because of the combination of Major triad and minor seventh interval, the notes of a Dominant seventh chord may not be taken from either a single Major or minor scale. Rather, the scale from which the notes of a Dominant seventh chord may be derived is the Mixolydian mode.
Now, the notes of Mixolydian are very similar to the notes of a Major scale with the exception of a very important flattened seventh scale degree.
Here are the notes of D Mixolydian.
If we play the first scale degree, D, together with the third scale degree, F-sharp, the fifth scale degree, A, and the seventh scale degree, C,
we will be playing the notes of a D Dominant seventh chord.
Similar to Major and minor seventh chords, Dominant seventh chords may also be constructed by following a specific pattern of intervals above a given note: Major third, minor third, minor third.
Let's use this interval pattern to construct a Dominant seventh chord above the note F. An interval of a Major third above the note F is the note A, an interval of a minor third above the note A is the note C, and an interval of a minor third above C is the note E-flat.