Triads and Seventh Chords: every key term you need (+ practice quiz)

More AP Music Theory guides

• Scales, Keys, and Intervals
• Harmonic Function and Voice Leading
• Harmonic Progressions and Cadences
• Secondary Function, Modulation, and Form

Triad

A three-note chord built in stacked thirds: root, third, and fifth.

Major Triad

Major 3rd plus minor 3rd (M3 + m3); root to fifth is a perfect 5th. Example: C–E–G.

Minor Triad

Minor 3rd plus major 3rd (m3 + M3); root to fifth is a perfect 5th. Example: C–E♭–G.

Diminished Triad

Two stacked minor 3rds; root to fifth is a diminished 5th. Example: B–D–F. Built on 7̂ in major and 2̂ in minor.

Augmented Triad

Two stacked major 3rds; root to fifth is an augmented 5th. Example: C–E–G♯. Can arise on III in harmonic minor.

Root Position

Chord voicing with the root as the lowest sounding pitch; figured bass 5/3 (usually left blank).

First Inversion

Chord voicing with the third in the bass; figured bass 6 (short for 6/3).

Second Inversion

Chord voicing with the fifth in the bass; figured bass 6/4; treated as unstable in common practice.

Seventh Chord

A four-note chord adding a seventh above the root to a triad.

Major Seventh Chord (M7)

Major triad plus major 7th above the root, e.g., C–E–G–B; built on I and IV in major.

Dominant Seventh Chord (Mm7)

Major triad plus minor 7th, e.g., G–B–D–F; built on 5̂, it contains the tritone that drives resolution to tonic.

Minor Seventh Chord (m7)

Minor triad plus minor 7th, e.g., D–F–A–C; built on ii, iii, and vi in major.

Half-Diminished Seventh Chord (ø7)

Diminished triad plus minor 7th, e.g., B–D–F–A; occurs on 7̂ in major and 2̂ in minor.

Fully Diminished Seventh Chord (o7)

Diminished triad plus diminished 7th — all minor 3rds, e.g., B–D–F–A♭; built on the leading tone in harmonic minor.

Third Inversion

Seventh-chord voicing with the seventh in the bass; figured bass 4/2 (or 2).

Figured Bass

Baroque shorthand: numbers below a bass note indicate intervals above it, implying chord and inversion (6 = first inversion, 6/4 = second).

Seventh-Chord Figures

Root position 7; first inversion 6/5; second inversion 4/3; third inversion 4/2.

Roman Numeral Analysis

Labels chords by the scale degree of their root; uppercase for major (I, IV, V), lowercase for minor (ii, vi), ° for diminished, + for augmented.

Diatonic Triads in Major

I, ii, iii, IV, V, vi, vii° — three major, three minor, one diminished.

Diatonic Triads in Minor

With harmonic-minor 7̂: i, ii°, III, iv, V, VI, vii° — V and vii° require the raised leading tone.

Chordal Seventh

The dissonant seventh of any seventh chord; it must be approached carefully and resolves down by step.

Doubling

In four voices a triad needs one repeated tone; double the root by default, and never double the leading tone or a chordal seventh.

Closed vs. Open Spacing

Closed (close) spacing packs the upper three voices within an octave; open spacing spreads them wider, with no gap over an octave between adjacent upper voices.

Arpeggio

The notes of a chord sounded one at a time rather than simultaneously.

Lead-Sheet Symbols

Popular-music chord labels above the staff: C = C major triad, Cm = minor, C7 = dominant seventh, Cmaj7 = major seventh, C°= diminished.

Chord Tone vs. Non-Chord Tone

Chord tones belong to the sounding harmony; any melody note outside the chord is a non-chord tone requiring classification.

Tendency Tone

A pitch with a strong pull: the leading tone rises to 1̂, the chordal seventh falls by step.

Triad Quality on Each Major Degree

Major on 1̂, 4̂, 5̂; minor on 2̂, 3̂, 6̂; diminished on 7̂.

Triad Quality in Natural Minor

Minor on 1̂, 4̂, 5̂; major on 3̂, 6̂, 7̂; diminished on 2̂ — but the dominant is usually made major by raising 7̂.

Inversion Symbols with Romans

Combined labels like V6/5 (dominant seventh, first inversion) or I6 (tonic triad, first inversion) show both function and bass note.

Picardy Third

A major tonic chord ending a piece in minor, created by raising 3̂ in the final chord.

Spacing Error

More than an octave between soprano–alto or alto–tenor voices; bass–tenor may exceed an octave.

Seventh Chord Qualities in Major

IM7, ii7, iii7, IVM7, V7, vi7, viiø7 — the dominant seventh appears only on 5̂.

Enharmonic Respelling of o7

A fully diminished seventh divides the octave into minor 3rds, so any of its four notes can act as the root when respelled.