What Are Diatonic Chords?

A scale provides a collection of notes. When you build chords using only those notes, you get a set of diatonic chords.

C major contains:

C–D–E–F–G–A–B

These notes produce seven triads:

C–Dm–Em–F–G–Am–Bdim

All seven chords are diatonic to C major because none of them contains a note outside the scale.

What is a diatonic scale?

A diatonic scale is a seven-note scale within an octave. It contains five whole steps and two half steps.

Diatonic scales include:

• the major scale;
• the natural minor scale;
• the seven diatonic modes.

For example, the C major scale is:

C–D–E–F–G–A–B–C

The distances between adjacent degrees are:

whole–whole–half–whole–whole–whole–half

A natural minor uses the same notes:

A–B–C–D–E–F–G–A

Its tonal center is A rather than C, so the scale degrees and chords take on different roles.

Harmonic and melodic minor contain altered scale degrees. Their chords can therefore differ from those of natural minor.

What does “diatonic” mean?

Diatonic means belonging to a chosen diatonic scale.

The word can describe notes, melodies, intervals, and chords.

In C major, the diatonic notes are:

C–D–E–F–G–A–B

F♯ is non-diatonic to C major because it does not belong to the scale.

In G major, however, F♯ is diatonic:

G–A–B–C–D–E–F♯

Diatonicity is therefore always defined in relation to a particular scale or key.

diatonic     = belongs to the chosen scale
non-diatonic = lies outside the chosen scale

What is a diatonic chord?

A diatonic chord contains only notes from the chosen diatonic scale.

For example, Dm contains:

D–F–A

All three notes belong to C major:

C–D–E–F–G–A–B

Dm is therefore diatonic to C major.

D major contains:

D–F♯–A

F♯ does not belong to C major, so D major is non-diatonic to that key.

The same D major chord is diatonic to D major:

D–E–F♯–G–A–B–C♯

A chord cannot be described as diatonic without context. You need to specify the scale or key to which it belongs.

How to build diatonic triads

Write out the notes of the scale, then build a three-note chord on every degree by taking every other note.

Starting on the first degree:

C–E–G

This produces a C major triad.

Starting on the second degree:

D–F–A

This produces Dm.

Starting on the third degree:

E–G–B

This produces Em.

When you reach the end of the scale, continue from its beginning.

For example, the triad built on the sixth degree is:

A–C–E

This produces Am.

Building a chord on every scale degree is called harmonizing the scale.

The diatonic triads of C major

The diatonic-triad pattern of a major key is:

I–ii–iii–IV–V–vi–vii°

Every major key contains:

• three major triads;
• three minor triads;
• one diminished triad.

The chord names change with the key, but their order and qualities remain the same.

Why the chords have different qualities

Every triad is built in the same way: take three alternating notes from the scale.

The intervals above each chord root, however, are different.

major triad:      1–3–5
minor triad:      1–♭3–5
diminished triad: 1–♭3–♭5

For example:

C    = C–E–G   = major triad
Dm   = D–F–A   = minor triad
Bdim = B–D–F   = diminished triad

The interval structure of these chords is explained in How Are Triads Built?.

How to read Roman numerals

A Roman numeral shows the scale degree on which the chord is built.

I  = chord built on the first degree
IV = chord built on the fourth degree
V  = chord built on the fifth degree

Uppercase and lowercase numerals show chord quality:

I  = major chord
ii = minor chord

The ° symbol marks a diminished triad:

vii°

In C major:

I     = C
ii    = Dm
iii   = Em
IV    = F
V     = G
vi    = Am
vii°  = Bdim

Roman numerals describe a chord’s position in the key rather than its specific name.

How to transpose chord progressions

Roman numerals preserve the structure of a progression when you change key.

Take this pattern:

I–vi–IV–V

In C major:

C–Am–F–G

In G major:

G–Em–C–D

The chord names change, but their relationships remain the same.

Roman numerals help you:

• move a song into a more comfortable key;
• compare progressions;
• remember harmonic structure;
• analyze music without relying on specific chord names.

Diatonic chords in natural minor

The same method works with the natural minor scale.

C natural minor contains:

C–D–E♭–F–G–A♭–B♭

Its diatonic triads are:

Cm–Ddim–E♭–Fm–Gm–A♭–B♭

The natural-minor pattern is:

i–ii°–III–iv–v–VI–VII

In minor-key harmony, the seventh degree is often raised.

In A natural minor, the chord built on the fifth degree is:

v = Em

Raising G to G♯ produces:

V  = E
V7 = E7

The major dominant creates a stronger pull toward the tonic chord, Am.

These chords use an altered scale degree, so they no longer belong entirely to the natural-minor collection.

Why diatonic chords sound connected

Diatonic chords draw from the same collection of notes.

For example:

C  = C–E–G
Am = A–C–E
F  = F–A–C
G  = G–B–D

Every note belongs to C major.

The progression:

C–Am–F–G
I–vi–IV–V

therefore remains inside one scale.

A shared note collection connects the chords, but it does not guarantee an effective progression.

The result also depends on:

• chord order;
• harmonic function;
• bass movement;
• inversions;
• rhythm;
• voice leading.

Diatonicity answers only one question:

Are the chords built from the notes of the chosen scale?

How chords relate to melody

When a melody and its chords come from the same scale, they share a common collection of notes.

Over the progression:

C–Am–F–G

you can use the notes of C major:

C–D–E–F–G–A–B

However, the same scale note can sound different over different chords.

For example, F:

• is a chord tone over F;
• creates tension over C;
• forms the seventh of a G7 chord.

The scale provides the general note collection. The current chord determines the role of each note at a particular moment.

Diatonic and non-diatonic chords

Compare two progressions in C major.

The first is:

C–F–G–C

Every chord is diatonic.

The second is:

C–F–D♭–C

D♭ major contains:

D♭–F–A♭

D♭ and A♭ do not belong to C major, so D♭ major is non-diatonic to the key.

A non-diatonic chord is not a mistake. It can function as:

• a borrowed chord;
• passing harmony;
• a chromatic chord;
• part of a modulation;
• a source of additional tension.

diatonic chord     - contains only notes from the chosen scale
non-diatonic chord - contains at least one note outside the scale

Diatonic seventh chords

The same principle applies to chords with more than three notes.

A triad uses three alternating scale notes:

1–3–5

A seventh chord adds one more:

1–3–5–7

From the first degree of C major:

C–E–G–B = Cmaj7

From the second degree:

D–F–A–C = Dm7

Both chords are diatonic to C major.

How to find the chords of a key

Take G major:

G–A–B–C–D–E–F♯

Build a triad on every scale degree:

G–B–D
A–C–E
B–D–F♯
C–E–G
D–F♯–A
E–G–B
F♯–A–C

Identify each chord:

G–Am–Bm–C–D–Em–F♯dim

Then label them with Roman numerals:

I–ii–iii–IV–V–vi–vii°

You can now use this chord set to analyze music and build progressions.

How Six Strings App can help

In Harmony, you can choose a key and see its scale, degrees, and diatonic chords.

Compare C major and G major. The chord names change, but the pattern remains:

I–ii–iii–IV–V–vi–vii°

In Chords, Arpeggios, and Scales, you can inspect the notes of any chord and view its fingerings.

In the Song Builder, you can create a progression, rearrange the chords, and hear the result.

Five-minute exercise

1. Write out the scale

G major:

G–A–B–C–D–E–F♯

2. Build the triads

Starting from each degree, take three alternating scale notes.

3. Check the result

G–Am–Bm–C–D–Em–F♯dim

4. Build a progression

Use the pattern:

I–vi–IV–V

In G major:

G–Em–C–D

5. Transpose it to D major

D–Bm–G–A

The chord names change, but the harmonic pattern remains the same.

Common mistakes

Calling every seven-note scale diatonic. A diatonic scale has a specific structure containing five whole steps and two half steps.

Treating “diatonic” as the name of a particular chord type. Diatonicity is always defined relative to a chosen scale.

Building chords without checking the notes of the scale. Scale harmonization must use notes from the chosen collection.

Assuming that diatonic chords can only be major or minor. The set also contains a diminished triad.

Confusing a scale degree with a chord built on that degree. 2 is the second scale degree. ii is the chord built on it.

Calling every chord that sounds appropriate diatonic. A chord can fit the music while still containing notes outside the scale.

Treating non-diatonic chords as mistakes. They extend the harmony but do not belong to the original note collection.

Treating natural minor as the only source of minor-key harmony. Minor keys often alter scale degrees to create stronger harmonic motion.

What to study next

• Scale Degrees in a Key — how notes and chords relate to the tonic.
• How Are Triads Built? — the interval structure of triads.
• Harmony — scales, chords, cadences, and modulations.
• What Is Chord Function? — the roles chords play within a key.
• Chords in a Major Key — the complete chord set of major keys.
• Chords in a Minor Key — chords from natural, harmonic, and melodic minor.

Short summary

A diatonic scale contains seven notes arranged as five whole steps and two half steps within an octave.

Diatonic notes and chords belong to the chosen scale.

To build diatonic triads, start on every degree and take three alternating scale notes.

The major-key pattern is:

I–ii–iii–IV–V–vi–vii°

The natural-minor pattern is:

i–ii°–III–iv–v–VI–VII

Non-diatonic chords are not mistakes. They simply contain notes outside the original scale.