Non-Diatonic Notes
YOASOBI’s もう少しだけ (Just a Little More) is built on a canon bass line in Eb major — almost entirely diatonic. But the moments that make it distinctive are the non-diatonic notes: chromatic passing chords, borrowed harmonies, and diminished approaches that briefly step outside the key. Play the interactive MIDI below and watch the orange (non-diatonic) and red (non-diatonic chord) highlights.
What Are Non-Diatonic Notes?
A diatonic note is one that belongs to the current key’s scale. In Eb major, the seven diatonic notes are:
\[E\flat \quad F \quad G \quad A\flat \quad B\flat \quad C \quad D\]Any other pitch — Db, E, F#, A, or B — is non-diatonic. These notes don’t belong to the key, so when they appear, they create tension, surprise, or color that the diatonic notes alone cannot provide.
Non-diatonic notes are not “wrong” notes. They are deliberate choices that serve specific harmonic functions: chromatic passing tones that connect two diatonic notes by half step, borrowed notes from a parallel key, or leading tones that create tension demanding resolution.
The Diatonic Foundation
Before examining what steps outside the key, it helps to see the diatonic framework. もう少しだけ is built on a canon bass line — a descending stepwise pattern through the Eb major scale:
\[E\flat \to D \to C \to B\flat \to A\flat \to G \to F \to B\flat\]Each bass note supports a diatonic chord:
| Bass | Chord | Degree | Function |
|---|---|---|---|
| Eb | Eb | I | Tonic |
| D | Bb/D | V/3 | Dominant, 1st inversion |
| C | Cm7 | vi7 | Relative minor |
| Bb | Bb | V | Dominant |
| Ab | Ab | IV | Subdominant |
| G | Eb/G | I/3 | Tonic, 1st inversion |
| F | Fm7 | ii7 | Supertonic |
| Bb | Bb | V | Dominant |
This progression repeats throughout the song. Every note in it belongs to Eb major — it is purely diatonic. The verse, chorus, and interlude all cycle through this pattern, and the interactive player colors all of these notes green.
Where Non-Diatonic Notes Appear
Chromatic Passing Chord: Bm7
In the Pre-Chorus, the canon bass line is interrupted by a chromatic insertion:
\[Cm7 \to Bm7 \to B\flat\]The bass walks C → B → Bb — three notes a half step apart. B natural is not in Eb major (the diatonic note between C and Bb is… nothing — they are a whole step apart). By inserting Bm7 between them, the composer fills the whole-step gap with a chromatic passing tone, creating a smooth half-step descent.
This is the most common type of non-diatonic chord: a chromatic passing chord that connects two diatonic chords by stepwise half-step motion. It exists only for voice leading — the ear accepts it because the bass motion is so smooth.
The same Bm7 reappears in the Interlude and Build sections, always serving the same function.
Chromatic Passing Chord in E Major: Cm
After the song modulates to E major for the Final Chorus, the same technique appears in the new key:
\[B/D\sharp \to Cm \to C\sharp m7\]Here C natural is the chromatic passing tone (not diatonic in E major), filling the half-step gap between B and C#. It is the exact same device as the Bm7 in Eb major, transposed up a half step.
Types of Non-Diatonic Notes
Non-diatonic notes fall into a few categories, all of which appear in popular music:
1. Chromatic Passing Tones
A note inserted between two diatonic notes a whole step apart, filling the gap with half steps. The Bm7 and Cm above are examples. The non-diatonic note is always brief and connects two diatonic targets.
2. Modal Interchange (Borrowing)
Chords borrowed from the parallel key (the key with the same tonic but opposite mode). In Eb major, the parallel key is Eb minor. Notes from Eb minor that differ from Eb major — like Gb, Cb, or Bbb — can be borrowed for a momentary darkening of the harmony.
3. Leading-Tone Approach
A chord built on a note a half step below its target, creating strong pull toward resolution. The leading tone of any major key (the 7th degree) is the most familiar example, but the technique can be applied to any target chord.
4. Modulation
When the entire key shifts, notes that were non-diatonic become diatonic and vice versa. もう少しだけ modulates from Eb major to E major for the Final Chorus — every pitch shifts up a half step, and the diatonic set changes from {Eb, F, G, Ab, Bb, C, D} to {E, F#, G#, A, B, C#, D#}. In the interactive player, you can see the highlighted diatonic rows shift at this point.
Why Non-Diatonic Notes Work
Non-diatonic notes work precisely because they contrast with the diatonic framework:
1. Tension and release. A non-diatonic note creates mild dissonance that the ear wants to resolve. When it resolves to a diatonic note (usually by half step), the release feels satisfying. The Bm7 → Bb resolution is a clear example.
2. Voice leading. Chromatic passing tones create the smoothest possible melodic motion — half steps. The bass line C → B → Bb moves more smoothly than C → Bb (a whole step), because each step is smaller.
3. Color without disruption. A single non-diatonic chord in an otherwise diatonic progression adds harmonic interest without destabilizing the key. The ear still perceives Eb major as home; the Bm7 is a brief visitor.
4. Expectation violation. Diatonic progressions are predictable — the ear learns the pattern quickly. Non-diatonic chords break the pattern just enough to recapture attention, which is why they tend to appear in pre-choruses and transitions rather than verses.