In this lesson
The seven triads built from a major scale follow this order: major, minor, minor, major, major, minor, diminished. In C major, they are C, Dm, Em, F, G, Am and B diminished. Roman numerals describe their roots and qualities: I, ii, iii, IV, V, vi and vii°.
You can work out this family from the scale’s notes. Then you can use the numerals to move a chord progression to another key. This lesson builds the chords in C and G major, followed by two guitar exercises using G, C, D and Em. You can do the written tasks before you know those shapes; the playing tasks assume you can form them slowly.
Build each chord from the scale
Start with the C major scale: C, D, E, F, G, A, B. Write it across two octaves so you have enough notes to keep counting:
C D E F G A B | C D E F G A B C
Choose a starting note, skip one scale note and take the next, then do that once more. From C, take C, skip D, take E, skip F, take G. C–E–G is C major.
From D, the same process gives D–F–A, which is D minor. Use the notes already in C major; changing F to F♯ would produce a different chord, D major, containing a note outside this scale.
These are triads: chords with three different notes arranged as a root, third and fifth. Those names count from the chord’s own root. D–F–A is root–third–fifth of D minor, while those same notes occupy degrees 2, 4 and 6 of C major.
The seven chords in C major
| Root’s scale degree | Chord notes | Chord name | Roman numeral |
|---|---|---|---|
| 1 | C–E–G | C major (C) | I |
| 2 | D–F–A | D minor (Dm) | ii |
| 3 | E–G–B | E minor (Em) | iii |
| 4 | F–A–C | F major (F) | IV |
| 5 | G–B–D | G major (G) | V |
| 6 | A–C–E | A minor (Am) | vi |
| 7 | B–D–F | B diminished (Bdim or B°) | vii° |
These are the diatonic triads of C major: all their notes belong to its scale. The repeated note names in the table can sit in different octaves.
Why does the quality change when the process stays the same? Scale steps have different sizes. C–E spans four semitones and C–G seven, giving a major triad. D–F spans three semitones and D–A seven, giving a minor triad. B–D spans three and B–F six, giving a diminished triad. The triad formulas explain those distances.
Read the Roman numerals
The numeral gives the scale degree of the chord’s root in the stated key. This lesson uses uppercase for major chords, lowercase for minor chords, and a small circle for diminished chords. Some charts use all capitals, so check their convention.
Read I as “one”, IV as “four”, V as “five” and vi as “six”. Include the quality when explaining a chord aloud: vi is the minor chord on degree 6.
Keep the key beside the numbers. V in C major is G major; V in G major is D major. A numeral on its own does not give a fixed chord name.
Degree 5 and chord V describe different things. In C major, degree 5 is the single note G. Chord V is the G major triad, G–B–D. The numeral also says nothing about which guitar string to use or how many beats to hold the chord.
Work out the chords in G major
G major uses G, A, B, C, D, E and F♯. Keep that F♯ when building every chord; the key-signature lesson explains its written signature.
| Roman numeral | Chord notes | Chord name |
|---|---|---|
| I | G–B–D | G major (G) |
| ii | A–C–E | A minor (Am) |
| iii | B–D–F♯ | B minor (Bm) |
| IV | C–E–G | C major (C) |
| V | D–F♯–A | D major (D) |
| vi | E–G–B | E minor (Em) |
| vii° | F♯–A–C | F♯ diminished (F♯dim) |
The chord names change, but the quality pattern stays I–ii–iii–IV–V–vi–vii° in every major key. For example, I–IV–V–I gives C–F–G–C in C major and G–C–D–G in G major.
Play I–IV–V–I on guitar
Use G major for this exercise so you can use open G, C and D shapes. Tune to standard tuning, E A D G B E from lowest to highest, with no capo. In the table, read strings 6 to 1 in that order. Numbers are fret numbers, 0 means an open string, and x means leave that string out.
| Chord | Low E, A, D, G, B, high E | Notes sounded, low to high |
|---|---|---|
| G | 3 2 0 0 0 3 |
G–B–D–G–B–G |
| C | x 3 2 0 1 0 |
C–E–G–C–E |
| D | x x 0 2 3 2 |
D–A–D–F♯ |
| Em, for the next exercise | 0 2 2 0 0 0 |
E–B–E–G–B–E |
A guitar shape can repeat notes across octaves. G still contains the three note names G, B and D even though you strum six strings. For finger positions, use the first-chord lesson.
Count four steady quarter-note beats per bar in 4/4. Strum down once on beat 1, then let the chord ring through beats 2, 3 and 4. Change on the following 1:
| Bar | Chord in G major | Numeral | Count |
|---|---|---|---|
| 1 | G | I | 1 2 3 4 |
| 2 | C | IV | 1 2 3 4 |
| 3 | D | V | 1 2 3 4 |
| 4 | G | I | 1 2 3 4 |
Strum G across all six strings, C from string 5, and D from string 4. After bar 4, stay on G and strike it again on the next beat 1 to restart bar 1. Each loop has four bars and sixteen beats.
You can use the metronome with four beats per bar and one click per numbered beat. Try 60 BPM and count one full bar before starting. Adjust the tempo as needed. If changing shapes interrupts the count, practise the movement separately with the chord-change drill.
Add a minor chord: I–V–vi–IV
Keep the same four-beat bars and one strike on each beat 1. Replace the previous chord order with:
| Bar | Chord in G major | Numeral |
|---|---|---|
| 1 | G | I |
| 2 | D | V |
| 3 | Em | vi |
| 4 | C | IV |
After C’s fourth beat, return to G on the next 1. Em is vi because its root E is degree 6 of G major and its triad is minor. Its notes E, G and B all belong to G major.
These are original practice loops, with the key and timing supplied. They are not transcriptions of a song. The beginner progression lesson gives further counted chord-change options.
Check your understanding
- What is chord ii in C major, and which notes make it?
- What is chord V in G major?
- Move I–V–vi–IV from G major to C major.
Answers
- D minor: D–F–A.
- D major: D–F♯–A.
- C–G–Am–F. The numeral pattern and qualities stay the same. This is a written transposition task; the guitar exercise above uses G major’s open shapes.
Can a song use chords outside its key?
Yes. The seven diatonic triads are a starting family, and music can use notes and chords outside that family. A D major chord contains F♯, which is outside C major, but that does not by itself make the chord a mistake or prove a key change. This lesson covers building triads from a major scale; analysing those other choices needs more context.
A chord list alone also cannot always establish a key. C and G occur in several keys. Here, the key is stated so that you can practise building and numbering chords without having to infer the tonal centre.
Sources and next steps
Robert Hutchinson’s Music Theory for the 21st-Century Classroom explains Roman-numeral chord symbols and the diatonic chord-quality pattern in major. Open Music Theory’s triad reference distinguishes chord roots, qualities and numeral conventions. The note tables and counted guitar exercises here were derived for this lesson.
Find C, E and G, the notes of chord I in C major, in a C major guitar scale pattern. Return to triads if you need more practice with major, minor and diminished qualities.