We also summarise the degree of the scale where each type of seventh chord occurs.
Dominant Seventh Chord
One area of confusion when naming or identifying seventh chords is the use of the term dominant seventh chord.
If you look at the table above summarising the degree of the scale where each type of seventh chord occurs, you will see that the dominant seventh need not lie only on the Vth degree of the scale, the degree we call the dominant. Indeed, in the natural minor scale, the dominant seventh chord lies on the VIIth degree not on the Vth degree.
The point to remember is that the dominant seventh chord is any chord formed by adding a minor seventh to a major triad. Remember too that the chord's note name is determined by its root note. So the chord G B D F is written G7 because the root note is G. G B D is a major triad and F is the minor seventh above G. This chord, therefore, is a dominant seventh chord.
In the key of C major, the notes G B D F form a seventh chord on the Vth degree, i.e. a dominant seventh on the dominant of the scale. This is also true for the C minor natural and C minor melodic scales. However, the same notes, G B D F, are a G7 chord and a dominant seventh on the fourth (IV) degree of the D melodic minor scale.
For completeness, we note finally that the notes G B D F are also a G7 chord and a dominant seventh on the seventh (VII) degree of the A natural minor scale.
Naming Seventh Chords
One useful convention for naming any seventh chord is:
root pitch letter, then chord tokens representing triad quality and seventh quality
For example, an Ab major minor 7 chord: the first term (Ab) tells us the root of the chord; the second term (major) identifies the quality of the triad that forms the lower three notes of the seventh chord; and, the third term (minor) identifies the quality of the interval of the seventh formed between the root and the seventh.