Seventh chords are merely triads (root, third and fifth) with the note an interval of a seventh above the root added.
In the early days of Western music, the addition of a seventh above the root of any given triad was used as an embellishment, also known as a color tone. Compositions then progressed in such a way that nearly every seventh chord became an unstable harmony; and therefore added forward motion with a gravitational pull towards resolution. The one exception to this concept is the major seventh chord, which often stands alone without the need for resolution as the tonic chord.
Major seventh chord
Major seventh chords are usually constructed on the first or fourth scale degree of the diatonic scale. Notated with the suffixes maj7, M7 & Δ it is comprised of the root, a major third, a perfect fifth, and a major seventh.
Dominant seventh chord
The dominant seventh chord is perhaps the most important seventh chord, as it is the first of its kind to appear in classical music. Notated with the suffix “7,” this chord’s gravitational pull is to resolve up a fourth (typically a V chord resolving to the tonic). It is comprised of the root, a major third, a perfect fifth, and a minor seventh.
Minor seventh chord
In a major key, minor seventh chords are typically built on the second, third or sixth scale degree. They consist of the root, minor third, perfect fifth, and minor seventh, and are notated with the suffixes min7, m7 & -7 .
Minor 7th (b5) chord
Comprised of the root, minor third, diminished fifth, and minor seventh, minor 7th (b5) chords are built upon the seventh degree of the major scale. They are notated with the suffixes -7 (♭5) & ø .
Fully diminished seventh chord
A fully diminished seventh chord is made of three superimposed minor thirds. This type of diminished chord contains a double-flatted seventh, whereas the half diminished seventh chord contains simply a single-flatted seventh. Notated by the suffixes °7 & dim7 , it is comprised of the root, minor third, diminished fifth, and diminished seventh.
An augmented triad is a chord consisting of two superimposed major thirds. Its name is derived from the fact that it is a major triad with a raised (or augmented) fifth. Noted by the suffixes aug & +, it is comprised of the root, major third, and augmented fifth.
The following exercise will be give you a workout of all of the various seventh chords we have covered. Sing through the outline of each seventh chord, and really concentrate on the intervallic relationship between each note. Incorporate this practice into your daily routine, and your tonal memory and ability to master these seventh chords will become greater each day.
Take it slow at first. The most important thing right now is to recognize where each pitch falls within the seventh chord.
You may repeat this exercise in chromatically ascending keys until the entire vocal range is covered. Take a moment to fill out the numbers of each note, if needed.