Chords and triads

A chord is two or more pitches sounding simultaneously. The most common chord type in Western music is the triad, a three-note chord built by stacking two thirds. Triads come in four qualities — major, minor, diminished, augmented — distinguished by the size of those two thirds.

Add a third on top of a triad and you have a seventh chord, the staple of jazz and late-Romantic harmony. Keep adding thirds and you arrive at ninth, eleventh, and thirteenth chords, all built from the same logic, just stacked higher.

Triads are the building blocks of tonal music. Every key produces seven diatonic triads, one on each scale degree, and every progression in the common-practice repertoire can be analysed as a sequence of those seven chords. Learning to recognise triad qualities by sound and by sight is the second great theoretical milestone after intervals.

A major triad consists of a major third on the bottom and a minor third on top: C-E-G. A minor triad reverses the order — minor third on the bottom, major on top — giving C-E-flat-G. A diminished triad stacks two minor thirds: C-E-flat-G-flat. An augmented triad stacks two major thirds: C-E-G-sharp. Those four arrangements account for every triad you will encounter in tonal music.

Major:       C — E — G        (M3 + m3)
Minor:       C — E♭ — G       (m3 + M3)
Diminished:  C — E♭ — G♭      (m3 + m3)
Augmented:   C — E — G♯       (M3 + M3)

Each quality has a characteristic feeling. Major is bright and stable; minor is darker but equally stable; diminished is unstable and demands resolution; augmented is suspended and ambiguous, often used as a transitional colour rather than a resting point.

Composers exploit these characters constantly — Schubert's Winterreise leans on minor triads to convey desolation; Debussy lets unresolved augmented chords float for entire bars; horror film scores use diminished triads to mark menace.

Every major key produces seven diatonic triads, one rooted on each scale degree. In C major: I (C major), ii (D minor), iii (E minor), IV (F major), V (G major), vi (A minor), vii° (B diminished). The Roman numeral pattern is universal — capitals for major, lowercase for minor, the small circle for diminished — and it lets musicians talk about progressions without committing to a key. A ii-V-I progression is the same harmonic gesture in every key.

• I — tonic, the home chord.
• ii — supertonic, frequent pre-dominant.
• iii — mediant, often a passing colour.
• IV — subdominant, the soft cousin of V.
• V — dominant, drives toward I.
• vi — submediant, the relative minor.
• vii° — leading-tone diminished, weak as a root chord but lovely in inversion.

A triad in root position has the root as the lowest note. Move the root up an octave and the third becomes the bass: this is first inversion, written with a 6 figure (or chord/3rd in modern slash notation). Move both root and third up and the fifth is in the bass: second inversion, figured 6/4. Inversions matter because the bass line drives a progression's character; voice leading often calls for a specific inversion to keep the bass moving smoothly.

Root position: C — E — G
First inversion: E — G — C   (write C/E)
Second inversion: G — C — E (write C/G)

A first-inversion triad is lighter and more passing; the bass moves stepwise, and the chord feels less anchored than in root position. A second-inversion triad is unstable and traditionally treated as a suspension that must resolve — a six-four chord on the cadential beat almost always resolves to V before going home. Composers from Bach to Schumann honour this convention; pop and jazz break it routinely, but the ear still hears the instability.

A triad written C-E-G can be voiced in many ways at the piano. Tight close-position voicings cluster all three notes inside an octave; open voicings spread them across two or more. A lead-sheet C major might be played left-hand C-G, right-hand E-G-C — the same chord, vastly more spacious. Voicing is half craft, half taste; the same progression sounds rich or thin depending on how the notes are distributed between the hands.

Doublings matter. In a four-voice texture you have one extra note to assign — usually the root, sometimes the fifth, rarely the third. Doubling the leading tone is a cardinal voice-leading error because both voices then want to resolve to the tonic and you end with parallel octaves. The three-voice triad becomes a four-voice voicing through a careful choice of doubling.

A suspended chord replaces the third with either a perfect fourth (sus4) or a major second (sus2), producing an open quality that resolves down to the third. Csus4 (C-F-G) resolves to C major (C-E-G); the F drops to E. Suspensions are the lifeblood of late-medieval and Renaissance music, and they remain central to modern pop and jazz. The ear recognises a suspension as tension; resolving it produces relief.

Stack a fourth third on top of a triad and you get a seventh chord. Stack a fifth and you get a ninth chord. Stack a sixth and you get an eleventh; a seventh, a thirteenth. By the time you reach a thirteenth chord, all seven scale degrees are present and the chord is essentially the whole key, voiced vertically.

The skill in voicing extended chords is selection: which notes to keep, which to omit, which to spread across the texture so the chord stays clear. See the seventh chords article for the next layer.