Theory · glossary
Diatonic
Also called diatonic chord, diatonic chords, in key, diatonic scale
Diatonic describes notes and chords that belong to a key's seven-note scale. In C major the diatonic notes are C D E F G A B, and the diatonic chords are C, Dm, Em, F, G, Am and Bdim.
Diatonic means “in the key”. A diatonic scale has seven notes, spaced by five whole steps and two half steps, with the two half steps as far apart as they can be. The major scale and the natural minor scale are the two most people meet first. Any note in that scale is diatonic to the key, and any chord built only from those notes is a diatonic chord. Notes and chords from outside the scale are called chromatic.
In C major the diatonic notes are the white keys of a piano, C D E F G A B. Stack every other note on each one (C E G, D F A, E G B and so on) and you get the key’s seven diatonic chords, shown here with their Roman numerals:
| Degree | C major | A minor |
|---|---|---|
| 1 | C (I) | Am (i) |
| 2 | Dm (ii) | Bdim (ii°) |
| 3 | Em (iii) | C (III) |
| 4 | F (IV) | Dm (iv) |
| 5 | G (V) | Em (v) |
| 6 | Am (vi) | F (VI) |
| 7 | Bdim (vii°) | G (VII) |
A minor uses the same seven notes as C major, starting from A, so it has the same chords with a different home. Many songs in A minor swap Em for E major (E G# B). That G# comes from the harmonic minor scale, and because it sits a half step below A, E major pulls back to Am harder than Em does.
A chord from outside the key stands out. In C major, an Ab major chord (Ab C Eb) has two notes from outside the scale, Ab and Eb. It is a borrowed chord, taken from C minor, and it brings a sudden darker color.
A “chords in the key of” chart lists exactly the diatonic chords of that key. They make a safe set to write with, because they all come from one scale. The chords in C major page lays them out with their sevenths, how to find the chords in any key shows the pattern that works in all 24 keys, and the online chord player lets you hear them.
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