Non-diatonic
Non-diatonic is the word for notes and chords that do not belong to the scale of the key. In C major every black key is at first non-diatonic. They come from another key or are chromatically altered. The opposite is called diatonic.
- Meaning
- does not belong to the scale of the key
- In C major
- all notes except C D E F G A B
- Typical examples
- secondary dominant, minor subdominant
- Opposite
- diatonic
Borrowed from outside
The seven notes of the scale and all chords built from them are diatonic. Non-diatonic is everything else. A non-diatonic note is a guest in the key. It can come from another key, like the F♯ in C major from G major or the A♭ from C minor, or be chromatically altered.
Secondary dominant D7 before G in C major
The chord D7 (D–F♯–A–C) contains F♯, which does not occur in C major. It is non-diatonic and leads like a dominant into the G major chord.
Minor subdominant F minor in C major
The chord F–A♭–C contains A♭, which comes from C minor. In major it is often borrowed as a colour before the close.
In the glossary: Diatonic · Alteration · Chromaticism
Listening
The first four chords show a secondary dominant placed in front of the dominant: D7 leads to G. The F♯ in it does not occur in C major, yet the progression sounds logical because D7 aims at G. Then follows a minor subdominant: the A♭ colours the close darker.
Non-diatonic is relative
Whether a note is non-diatonic depends on the key. F♯ is foreign in C major, native in G major. If a non-diatonic harmony stays and becomes the new reference point, one speaks of modulation. If it is only touched briefly it is a colouring.
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Related terms
DiatonicAlterationChromaticismDiatonic chordKeyModulationDominantSubdominant
Editor: Maik Krohm · reviewed on 3 October 2026
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