Topic 3.3 Seventh Chords: build a seventh chord by adding a seventh above the root, and identify its quality (major, dominant, minor, half-diminished, fully diminished).

What this topic is asking

The College Board (Topic 3.3) wants you to build a seventh chord by adding a seventh above the root of a triad and to identify its quality among the five common types: major seventh, dominant (major-minor) seventh, minor seventh, half-diminished seventh and fully diminished seventh. The quality comes from the triad below plus the size of the seventh.

A triad plus a seventh

Because it is a stack of four thirds, a seventh chord in root position appears as four notes all on lines or all on spaces. Spell it by skipping a letter each time: C skip D to E skip F to G skip A to B gives C, E, G, B.

The five common qualities

The course focuses on five seventh-chord qualities, each a combination of triad quality and seventh size:

• Major seventh (M7): major triad plus a major seventh. Example C, E, G, B.
• Dominant seventh (Mm7, or major-minor seventh): major triad plus a minor seventh. Example G, B, D, F.
• Minor seventh (m7): minor triad plus a minor seventh. Example C, E flat, G, B flat.
• Half-diminished seventh: diminished triad plus a minor seventh. Example B, D, F, A.
• Fully diminished seventh: diminished triad plus a diminished seventh. Example B, D, F, A flat.

Diatonic seventh chords

Built on each degree of a major scale using only the key's notes, the seventh chords give a fixed pattern of qualities: major seventh on degrees 1 and 4, dominant seventh on degree 5, minor seventh on degrees 2, 3 and 6, and half-diminished seventh on degree 7. This is why the chord on the dominant (degree 5) is the dominant seventh: the diatonic seventh above the leading tone is minor over a major triad. In harmonic minor the chord on degree 7 becomes a fully diminished seventh because the raised leading tone produces a diminished seventh above it.

Why the seventh adds tension

The central idea is that the seventh is a dissonance added to a stable triad, and dissonance creates motion. The seventh of a chord is heard as an unstable tone that wants to resolve down by step, which is why the dominant seventh drives so strongly to the tonic: its seventh (the subdominant degree) falls to the third of the tonic chord, while its third (the leading tone) rises to the tonic. Naming a seventh chord correctly therefore tells you not just what it is but what it will probably do next. This is the link between the spelling skill here and the voice-leading rules later: the part-writing questions reward resolving the chordal seventh down by step, and you can only do that if you have first identified which note is the seventh.

Building a seventh chord

To build a seventh chord, write the four alternate letters (root, third, fifth, seventh), set the triad quality with accidentals, then adjust the top note so the seventh above the root is the size you want.

Try this

Q1. What two ingredients make a half-diminished seventh chord? [1 point]

• Cue. A diminished triad plus a minor seventh above the root (for example B, D, F, A).

Q2. Build the minor seventh chord on E and name its four pitches. [2 points]

• Cue. E, G, B, D: a minor triad (E, G, B) plus a minor seventh (D), all natural notes.