Section 8.1 Introduction to Seventh Chords
A seventh chord adds to a triad another note a third higher than the fifth. Chords, being built in thirds, have members that are odd numbers—third, fifth, seventh, and we will eventually discuss extensions of the ninth, eleventh, and thirteenth. The fifteenth would be the double octave, so chords only extend as high as the thirteenth.
In classical and popular music, there are five types of seventh chords commonly encountered:
the major seventh chord
the major-minor seventh chord (also known as a dominant seventh chord)
the minor seventh chord
the half-diminished seventh chord
the fully-diminished seventh chord (often called diminished seventh chord)
Another way to differentiate between the five types of seventh chords is by learning how the thirds are stacked in each one.
In later chapters we will discuss other seventh chords built on augmented triads and minor triads.