Chord Construction – Building Chords | Music Theory

Fundamentals: Intervals and Overlapping

Chords are built by stacking thirds. This principle, known as ‘stacked thirds’ (tertian harmony), forms the basis of all Western harmony. Understanding how it works enables you to build any chord starting from a single note.

Major Third (M3)

An interval of 4 semitones (2 tones). A bright, open sound.

Examples:

C → E (4 semitones)
G → B (4 semitones)
F → A (4 semitones)

Minor Third (m3)

An interval of 3 semitones (1½ tones). A dark, rich tone.

Examples:

C → E flat (3 semitones)
A → C (3 semitones)
E → G (3 semitones)

The Principle of the Superposition of Terths

Starting from the root note, each new note adds a third above the previous one. The more thirds you stack, the more complex the chord becomes:

13a+ third

11a+ third

9a+ third

7a+ third

5a+ third

3a+ third

Essential (1)

Triad: 1-3-5

Seventh: 1-3-5-7

Extended: 1-3-5-7-9-11-13

Key Concept

The combination of major and minor thirds determines the quality of the chord. M3 + m3 = major, m3 + M3 = minor, m3 + m3 = diminished, M3 + M3 = augmented. This principle applies to all chords, from the simplest to the most complex.

Triad — The Foundations

Triads are three-note chords and form the basis on which all more complex chords are built. Each triad consists of a root (1), a third (3) and a fifth (5). The quality of the third and the fifth determines the type of triad.

Major

1 - 3 - 5

M3 + m3 (4+3 semitones)

C: C - E - G

Minor

1 - b3 - 5

m3 + M3 (3+4 semitones)

Chords: C – E♭ – G

Reduced

1 - b3 - b5

m3 + m3 (3+3 semitones)

C°: C – Eb – Gb

Increased

1 - 3 - #5

M3 + M3 (4+4 semitones)

C+: C - E - G#

Suspended 2 (sus2)

1 - 2 - 5

M2 + P4 (2+5 semitones)

Csus2: C – D – G

Suspended 4 (sus4)

1 - 4 - 5

P4 + M2 (5+2 semitones)

Csus4: C – F – G

Complete Table of Triads in All Keys

Found.	Major	Minor	Reduced	Increased
C	C - E - G	C – Eb – G	C – Eb – Gb	C - E - G#
C#/Db	Db – F – Ab	C# - E - G#	C# - E - G	Db – F – A
D	D - F# - A	D - F - A	D – F – Ab	D - F# - A#
Eb	Eb – G – Bb	Eb – Gb – Bb	Eb – Gb – A	Eb – G – B
E	E - G# - B	E - G - B	E – G – Bb	E - G# - C
F	F - A - C	F – Ab – C	F – Ab – B	F - A - C#
F#/Gb	F# - A# - C#	F# - A - C#	F# - A - C	F# - A# - D
G	G - B - D	G – Bb – D	G – Bb – Db	G - B - D#
Ab	Ab – C – Eb	Ab – B – Eb	A–B–D	A – C – E
A	A - C# - E	A - C - E	A – C – Eb	A - C# - F
Bb	Bb – D – F	Bb – Db – F	Bb – Db – E	Bb – D – F#
B	B - D# - F#	B - D - F#	B - D - F	B - D# - G

Note on Suspended Chords

Sus2 and sus4 chords do not contain the third, so they are neither major nor minor. The term ‘suspended’ refers precisely to this tonal ambiguity: the third is ‘suspended’ upwards (sus4 = fourth) or downwards (sus2 = second). They typically resolve to the corresponding major or minor chord.

Seventh chords

By adding a fourth note (the seventh) to the triad, we obtain seventh chords. These chords have a richer and more complex sound, and are fundamental in jazz, classical music and modern pop. The type of seventh (major or minor), combined with the type of triad, gives rise to different families of seventh chords.

Maj7 – Major Seventh

1 - 3 - 5 - 7

Major triad + major seventh. A gentle, dreamy, sophisticated sound.

Cmaj7: C – E – G – B

Used in jazz, bossa nova and R&B; a chord consisting of the first and fourth degrees in major keys.

7 – Seventh Dominant

1 - 3 - 5 - b7

Major triad + minor seventh. A tense, energetic sound, seeking resolution.

C7: C – E – G – Bb

The V chord. Essential in blues, jazz and funk. It creates tension towards the tonic.

m7 – Minor seventh

1 - b3 - 5 - b7

Minor triad + minor seventh. A warm, mellow, jazzy sound.

Cm7: C – Eb – G – Bb

Chords in the ii, iii and vi degrees. A staple of jazz, soul and neo-soul.

m7b5 – Half-diminished

1 - b3 - b5 - b7

Diminished triad + minor seventh. A tense, incomplete sound.

Cm7b5: C – Eb – Gb – Bb

VII major, ii minor. Essential in minor ii-V-I progressions.

°7 – Diminished Seventh

1 - b3 - b5 - bb7

Diminished triad + diminished seventh. A symmetrical chord, consisting solely of minor thirds.

C°7: C – Eb – Gb – A

Chromatic progression. Just 3 unique dim7 chords (symmetry!).

mMaj7 – Minor with major 7th

1 - b3 - 5 - 7

Minor triad + major seventh. A mysterious, cinematic sound.

CmMaj7: C – Eb – G – B

The first scale degree of the melodic minor scale. Used in jazz and film soundtracks.

Comparison of Seventh Chords (from C)

Symbol	Name	Formula	Notes (C)	Semitones
Cmaj7	Major seventh	1 - 3 - 5 - 7	C - E - G - B	4 - 3 - 4
C7	Dominant seventh	1 - 3 - 5 - b7	C – E – G – Bb	4 - 3 - 3
Cm7	Minor seventh	1 - b3 - 5 - b7	C – Eb – G – Bb	3 - 4 - 3
Cm7b5	Semi-diminished	1 - b3 - b5 - b7	C – Eb – Gb – Bb	3 - 3 - 4
C°7	Diminished seventh	1 - b3 - b5 - bb7	C – Eb – Gb – A	3 - 3 - 3
CmMaj7	Minor-major 7	1 - b3 - 5 - 7	C – Eb – G – B	3 - 4 - 4

Extended Agreements

Extended chords include notes beyond the seventh: the ninth (9th), the eleventh (11th) and the thirteenth (13th). These chords form the basis of jazz harmony and lend a richness of sound that is impossible to achieve with triads or seventh chords alone.

How Extensions Work

The 9th corresponds to the 2nd an octave higher. The 11th corresponds to the 4th an octave higher. The 13th corresponds to the 6th an octave higher. In practice: 9 = 2 + 7, 11 = 4 + 7, 13 = 6 + 7. A full 13th chord contains all 7 notes of the scale!

Ninth (9) chords

Cmaj9

1 - 3 - 5 - 7 - 9

C - E - G - B - D

C9

1 - 3 - 5 - b7 - 9

C – E – G – Bb – D

Cm9

1 - b3 - 5 - b7 - 9

C – Eb – G – Bb – D

Eleventh (11) Chords

Cmaj9(#11)

1 - 3 - 5 - 7 - 9 - #11

C - E - G - B - D - F#

C11

1 - 3 - 5 - b7 - 9 - 11

C – E – G – Bb – D – F

Cm11

1 - b3 - 5 - b7 - 9 - 11

C – Eb – G – Bb – D – F

Thirteenth (13) Chords

Cmaj13

1 - 3 - 5 - 7 - 9 - 13

C - E - G - B - D - A

C13

1 - 3 - 5 - b7 - 9 - 13

C – E – G – Bb – D – A

13 cm

1 - b3 - 5 - b7 - 9 - 13

C – Eb – G – Bb – D – A

Notes to Avoid

Some extensions create unwanted dissonance with the notes of the root chord. These are called ‘avoid notes’ because, if held, they obscure the quality of the chord.

Agreement	Note to be avoided	Reason
Maj7	11 natural (4a)	B9 chord with the major third (e.g. F against E in Cmaj7)
Sun 7	It depends on the context	The dominant chord accepts almost all intervals, even altered ones
m7 (on Grade III)	b13 (b6)	B9 chord with a perfect fifth
m7 (on grade VI)	b9 e b13	Both create strong dissonances

Practical Tip

In practice, extended chords often omit certain intermediate notes. A C13 typically includes: the root, 3rd, b7th, 9th and 13th, omitting the 5th and 11th. The important thing is that the highest note (the extension) is present. The root may be omitted if played from the bass.

Altered Chords

Altered chords modify (raising or lowering by a semitone) one or more notes of the dominant chord. They are extremely powerful tools for creating maximum tension before resolution and form the heart of advanced jazz harmony.

The Four Accidental Alterations

b9 Flat ninth

C7b9: C – E – G – Bb – Db. A dark sound with strong tension. Common in resolutions to minor chords.

#9 Sharp 9th

C7#9: C – E – G – Bb – D#. The famous ‘Hendrix chord’! An aggressive, bluesy sound.

#11 Eleventh sharp

C7#11: C – E – G – Bb – F#. A Lydian-dominant sound, sophisticated and modern.

b13 Thirteenth flat

C7b13: C – E – G – Bb – Ab. Melodic tension, often combined with b9 or #9.

The Altered Chord (7alt)

The ‘alt’ chord (e.g. C7alt) contains all possible accidents: b9, #9, #11 (= b5) and b13 (= #5). It corresponds to the superlocrian scale (the 7th mode of the melodic minor scale).

1 - 3 - b7 - (b9 #9 #11 b13)

C7alt: C – E – Bb + any combination of Db, D#, F#, Ab

Altered C scale: C – D♭ – D♯ – E – F♯ – Ab – Bb – C
(Corresponds to the ascending melodic D♭ minor scale)

Common Altered Combinations

Symbol	Formula	Notes (C)	Typical use
C7b9	1 - 3 - 5 - b7 - b9	C – E – G – Bb – Db	V7 → minor
C7#9	1 - 3 - 5 - b7 - #9	C – E – G – Bb – D#	Blues, funk, rock
C7#11	1 - 3 - 5 - b7 - #11	C – E – G – Bb – F#	Dominant Lydian
C7b9b13	1 - 3 - 5 - b7 - b9 - b13	C – E – G – Bb – Db – Ab	Dominant Phrygian mode
C7#9b13	1 - 3 - b7 - #9 - b13	C – E – Bb – D# – Ab	Partially altered
C7alt	1 - 3 - b7 - (all alternatives)	C – E – Bb – Db/D# – F# – Ab	Completely altered