AP® Music Theory · Unit 3 · Topic 3.2
Diatonic Triads in a Minor Key
A minor key gives more than seven possible triads because natural minor and harmonic minor each build their own stack of thirds, and the raised seventh degree swaps the minor v chord for a major V with real pull to the tonic.
Triads in a key come from stacking the scale's own notes in thirds above each scale degree. A major key has one scale, so it has one set of seven diatonic triads. A minor key is different: natural minor has an unraised seventh degree, but harmonic minor raises that seventh degree by a half step to create a stronger pull toward the tonic. Since both versions of minor are in common use, a minor key effectively offers two overlapping sets of diatonic triads, more than seven possible chords built on seven scale degrees.
The raised leading tone changes the v chord directly. In natural minor, the triad on scale degree 5 is minor, because its third (built on scale degree 7) sits only a whole step below the tonic. Raise that seventh degree by a half step, as harmonic minor does, and the third of the v chord rises a half step too, turning the minor third into a major third. The chord is now V, major, with its third sitting a half step below the tonic, right where a leading tone needs to be to pull strongly upward into the tonic at a cadence.
This raised seventh degree does not only affect the triad built on scale degree 5. The same note is the third of the chord built on scale degree 3, so raising it changes that chord's quality as well, usually from major to augmented. Both effects come from the same single half-step change, which is why harmonic minor, not natural minor, supplies the chords used for strong cadences.
Key terms
- natural minor
- The minor scale using only the key's unaltered notes, with no raised seventh degree.
- harmonic minor
- The minor scale with the seventh degree raised a half step to create a leading tone.
- leading tone
- A scale degree a half step below the tonic that pulls strongly toward resolving to it.
- diatonic triad
- A three-note chord built entirely from the notes of a given key or scale.
- cadence
- A chord progression that closes a musical phrase, often ending on the tonic.
Watch it explained
- How it worksHow does raising the leading tone turn the minor v chord into a major V?
- Worked exampleFind all the diatonic triads in A minor using natural minor and then using harmonic minor.
- Common mistakeWhy doesn't the natural minor v chord work at a strong cadence?
- Going furtherWhat happens to the chord on scale degree 3 once the leading tone gets raised?
Check yourself
End of topic.