Harmony: Triads and Chords

A triad is a three-note chord built by stacking two thirds above a root note. The four triad qualities are major (M3+m3), minor (m3+M3), diminished (m3+m3), and augmented (M3+M3). Each quality has a distinctive sound character.

A seventh chord adds a fourth note a third above the fifth of a triad. The five common types are: major 7th (M3+m3+M3), dominant 7th (M3+m3+m3), minor 7th (m3+M3+m3), half-diminished 7th (m3+m3+M3), and fully diminished 7th (m3+m3+m3).

A chord inversion occurs when a note other than the root is the lowest-sounding pitch (bass note). Root position has the root in the bass. First inversion has the third in the bass. Second inversion has the fifth in the bass. Seventh chords also have third inversion with the seventh in the bass.

Figured bass uses numbers below a bass note to indicate the intervals above it, specifying chord inversions. Root position triad = 5/3 (often no figures). First inversion = 6/3 (written as 6). Second inversion = 6/4. For seventh chords: root = 7, first = 6/5, second = 4/3, third = 4/2 (or 2).

Diatonic triads are chords built using only the notes of a given key. In Roman numeral analysis, uppercase numerals indicate major triads and lowercase indicate minor triads. A degree symbol indicates diminished and a plus sign indicates augmented.

Diatonic seventh chords are four-note chords built on each scale degree using only notes from the key. Each scale degree produces a specific seventh chord quality, creating a unique set of sounds for major and minor keys.

Every diatonic chord serves one of three harmonic functions. Tonic chords (I, vi, iii) provide stability and rest. Predominant chords (IV, ii) create momentum toward the dominant. Dominant chords (V, vii-dim) create tension that resolves to the tonic.

Chord quality is determined by the specific combination of intervals stacked from the root. By knowing the interval structure, you can build any chord quality from any root note without memorizing every individual chord.