Section 27.5 When to Use Seventh Chords
In your harmonizations of melodies, it is best to use seventh chords to add tension as you approach tonic function. Therefore, sevenths are added most frequently to chords of dominant function (\(\left.\text{V}\right.\) and \(\left.\text{vii}^{\circ}{}\right.\)) and chords of pre–dominant function (\(\left.\text{ii}\right.\) and, to a lesser extent, \(\left.\text{IV}\right.\)). (See the harmonic flowchart.) For this reason, seventh chords like \(\left.\text{iii}^{7}\right.\), \(\left.\text{vi}^{7}\right.\), \(\left.\text{IV}\text{M}^{7}\right.\), and \(\left.\text{I}\text{M}^{7}\right.\) are less commonly used and encountered.
