Diatonic Chords
Diatonic chords are the 7 chords you can build using only the notes of a scale. In every major key, the pattern is the same: I-ii-iii-IV-V-vi-vii° — three major, three minor, and one diminished. These 7 chords form the harmonic vocabulary of a key.
Building Chords from a Scale
To build diatonic chords, take each note of the scale as a root, then stack two more notes by skipping every other scale note. You only use notes that are in the scale.
For C major (C D E F G A B):
| Degree | Chord | Quality | Roman |
|---|---|---|---|
| 1st | C major | Major | I |
| 2nd | D minor | Minor | ii |
| 3rd | E minor | Minor | iii |
| 4th | F major | Major | IV |
| 5th | G major | Major | V |
| 6th | A minor | Minor | vi |
| 7th | B diminished | Diminished | vii° |
Why Each Chord Has Its Quality
The qualities are not arbitrary — they are a mathematical consequence of the scale. The ii chord in C major must be minor because the available notes (D, F, A) naturally form a minor triad. You would need F# to make D major, but F# is not in the C major scale. The chord qualities are determined by the scale, not chosen.
This same pattern — major, minor, minor, major, major, minor, diminished — applies to every major key. In G major the chords are G, Am, Bm, C, D, Em, F#dim. Different notes, same pattern.
In ChordColor
When you select a key and scale, the KEY row displays all 7 diatonic chords with their Roman numerals. Click any chord to see its voicings and colors on the current instrument. Switch scales to see how the pattern changes — natural minor gives i-ii°-III-iv-v-VI-VII.