How to Harmonise the Major Scale
Harmonising a scale means building a chord from each of its notes using only notes that belong to that scale.
When we harmonise the major scale, each scale degree produces a particular chord quality. This gives us the family of chords naturally associated with a major key.
In this lesson, you will learn how to:
- Build triads from each degree of the major scale
- Understand why the chord qualities change
- Label chords using Roman numerals
- Apply the same pattern in different keys
- Extend the process to seventh chords
What Does Harmonising a Scale Mean?
A scale gives us an ordered collection of notes. Harmonising it means building a chord on each degree of the scale using only notes from that scale.
In this context, diatonic means that every note in each chord belongs to the major scale being harmonised.
To build the triads, treat each of the seven scale degrees as a new root and select every other note until you have a root, 3rd and 5th. For the later scale degrees, continue into the next octave where needed.
Using C major:
C–E–G
D–F–A
E–G–B
F–A–C
G–B–D
A–C–E
B–D–F
This produces one triad from each degree of the scale.
Building Triads from C Major
The C major scale contains:
C – D – E – F – G – A – B
To harmonise it, build a triad from each scale degree using only notes from the scale.
| Scale degree | Notes | Chord |
|---|
| 1 | C – E – G | C major |
| 2 | D – F – A | D minor |
| 3 | E – G – B | E minor |
| 4 | F – A – C | F major |
| 5 | G – B – D | G major |
| 6 | A – C – E | A minor |
| 7 | B – D – F | B diminished |
The resulting chord-quality pattern is:
Major – Minor – Minor – Major – Major – Minor – Diminished
This pattern remains the same in every major key.
Why Do the Chord Qualities Change?
Each chord is built using the same method: begin on a scale degree and take every other note. The chord qualities change because the intervals between those notes are not identical.
C Major
C – E – G
C to E is a major 3rd. C to G is a perfect 5th.
1 – 3 – 5
D Minor
D – F – A
D to F is a minor 3rd. D to A is a perfect 5th.
1 – ♭3 – 5
B Diminished
B – D – F
B to D is a minor 3rd. B to F is a diminished 5th.
1 – ♭3 – ♭5
Although every chord is built by stacking thirds from the scale, the changing interval distances produce different chord qualities.
Chord Qualities and Roman Numerals
Roman numerals allow us to describe chords by their position within a key rather than by their specific note names.
Uppercase Roman numerals represent major chords: I, IV and V. Lowercase numerals represent minor chords: ii, iii and vi. A small degree symbol identifies the diminished chord: vii°.
| Scale degree | Roman numeral | Chord quality |
|---|
| 1 | I | Major |
| 2 | ii | Minor |
| 3 | iii | Minor |
| 4 | IV | Major |
| 5 | V | Major |
| 6 | vi | Minor |
| 7 | vii° | Diminished |
I – ii – iii – IV – V – vi – vii°
Why Roman Numerals Are Useful
Chord names change in a different key, but Roman numerals preserve the scale-degree relationship. I–IV–V is C–F–G in C major and G–C–D in G major.
- Analyse chord progressions
- Compare music in different keys
- Transpose progressions
- Understand how chords relate to the tonic
- Communicate chord structures without relying on one specific key
Applying the Pattern to G Major
The G major scale contains:
G – A – B – C – D – E – F♯
| Degree | Roman numeral | Notes | Chord |
|---|
| 1 | I | G – B – D | G major |
| 2 | ii | A – C – E | A minor |
| 3 | iii | B – D – F♯ | B minor |
| 4 | IV | C – E – G | C major |
| 5 | V | D – F♯ – A | D major |
| 6 | vi | E – G – B | E minor |
| 7 | vii° | F♯ – A – C | F♯ diminished |
The chord names and notes have changed, but the sequence of qualities remains the same.
Building Progressions from the Harmonised Scale
Once the major scale has been harmonised, its chords can be combined to create progressions.
I–IV–VC – F – G
I–V–vi–IVC – G – Am – F
ii–V–IDm – G – C
The Roman numerals describe where each chord comes from within the key. They do not tell you how long each chord should last or how it must be played; they describe the underlying chord relationship.
Harmonising the Major Scale with Seventh Chords
By stacking one more diatonic third above each triad, we create seventh chords:
Root – 3rd – 5th – 7th
Each chord now contains four different chord tones.
Seventh Chords in C Major
| Degree | Roman numeral | Notes | Chord |
|---|
| 1 | Imaj7 | C – E – G – B | Cmaj7 |
| 2 | iim7 | D – F – A – C | Dm7 |
| 3 | iiim7 | E – G – B – D | Em7 |
| 4 | IVmaj7 | F – A – C – E | Fmaj7 |
| 5 | V7 | G – B – D – F | G7 |
| 6 | vim7 | A – C – E – G | Am7 |
| 7 | viiø7 | B – D – F – A | Bm7♭5 |
The seventh chords follow this pattern:
Major 7 – Minor 7 – Minor 7 – Major 7 – Dominant 7 – Minor 7 – Half-Diminished 7
Why the V Chord Becomes a Dominant 7th
The seventh chord built from the fifth degree contains 1 – 3 – 5 – ♭7, the formula for a dominant 7th chord. In C major, G–B–D–F produces G7.
The chord contains a strong tension between B and F. That tension often resolves when the music moves back to C major.
Triads and Seventh Chords Compared
| Degree | Triad | Seventh chord |
|---|
| I | Major | Major 7 |
| ii | Minor | Minor 7 |
| iii | Minor | Minor 7 |
| IV | Major | Major 7 |
| V | Major | Dominant 7 |
| vi | Minor | Minor 7 |
| vii° | Diminished | Half-diminished 7 |
The seventh chord keeps the original triad and adds one more scale note a third above the fifth.
Why Harmonising the Major Scale Matters
Harmonising the major scale reveals the family of chords naturally associated with a major key.
- Build the diatonic chords of any major key
- Understand where chords within a key come from
- Label progressions using Roman numerals
- Move progressions into different keys
- Recognise common chord relationships
- Extend triads into seventh chords
- Begin understanding chord function and resolution
You do not need to memorise the chords of every key separately. Learn I – ii – iii – IV – V – vi – vii°, then apply it to any major scale.
Practice Exercise
Try harmonising the G major scale without using the completed table above.
- Write out the notes of G major.
- Build a triad from each scale degree by selecting every other note.
- Identify the interval formula of each chord.
- Name the chord quality.
- Label each chord with a Roman numeral.
- Extend each triad by adding another diatonic third.
- Compare your results with the major-key quality patterns.
Quick Test
Click each question to reveal the answer.
What does it mean to harmonise a scale?
Build a chord from each scale degree using only notes from that scale.
How is a triad built from a scale degree?
Begin on that degree and select every other scale note: root, 3rd and 5th.
What is the sequence of triad qualities produced by the major scale?
Major, minor, minor, major, major, minor and diminished.
Why is the chord built on the seventh degree diminished?
Its notes produce the interval formula 1–♭3–♭5.
What do uppercase and lowercase Roman numerals represent?
Uppercase represents major chords and lowercase represents minor chords.
What are the I, IV and V chords in G major?
G major, C major and D major.
How do you extend a diatonic triad into a seventh chord?
Add another diatonic third above the fifth.
What is the seventh-chord quality pattern of the major scale?
Major 7, minor 7, minor 7, major 7, dominant 7, minor 7 and half-diminished 7.
If chord construction is unfamiliar, review Introduction to Triads. To inspect the notes and voicings of any resulting chord, use the Guitar Chord Finder.
