The Pentatonic Scale
Yorushika’s 藍二乗 (Deep Indigo) is built on a driving rock arrangement, but 95% of its lead melody uses only five notes — the D# minor pentatonic scale. It is a clean demonstration of why the pentatonic scale works so well over diatonic harmony. Play the interactive MIDI below and watch the green (pentatonic) and orange (non-pentatonic) notes.
What Is the Pentatonic Scale?
The pentatonic scale is a five-note scale found in virtually every musical tradition worldwide. In the context of Western harmony, it is the major (or minor) scale with two notes removed: the 4th and the 7th degrees.
In F# major, the full diatonic scale is:
\[F\sharp \quad G\sharp \quad A\sharp \quad B \quad C\sharp \quad D\sharp \quad E\sharp\]The F# major pentatonic removes B (4th) and E# (7th):
\[F\sharp \quad G\sharp \quad A\sharp \quad C\sharp \quad D\sharp\]Rewritten starting from D# (the relative minor), this is the D# minor pentatonic:
\[D\sharp \quad F\sharp \quad G\sharp \quad A\sharp \quad C\sharp\]Same five pitches, different starting point. This dual identity — simultaneously major and minor — is the first clue to why the scale is so versatile.
Why Remove the 4th and 7th?
The 4th and 7th degrees of the major scale are the two notes that form a tritone — the most dissonant interval in tonal music. In F# major, B and E# are a tritone apart. These are also the notes responsible for the strongest harmonic tensions: E# is the leading tone that pulls toward F#, and B is the subdominant that pulls toward A#.
By removing these two notes, the pentatonic scale eliminates:
- All tritone intervals within the scale
- All half-step intervals (every pentatonic interval is a whole step or minor 3rd)
- All notes that create strong dissonance against common chord tones
The result is a scale that is maximally consonant — five notes, zero harsh clashes.
Pentatonic Notes Against Every Chord
The core insight: a pentatonic melody plays the same five notes regardless of which chord is underneath, and it always sounds good. Here is why — using the four chords in 藍二乗 (the I → vi → IV → V loop in F# major):
| Pentatonic Note | Over F# (I) | Over C# (V) | Over D#m (vi) | Over B (IV) |
|---|---|---|---|---|
| D# | 6th | 2nd (sus) | Root | 3rd |
| F# | Root | 4th (sus) | b3rd | 5th |
| G# | 2nd (add9) | 5th | 4th (sus) | 6th |
| A# | 3rd | 6th | 5th | 7th (maj7) |
| C# | 5th | Root | b7th | 2nd (add9) |
Every pentatonic note is either a chord tone (root, 3rd, 5th) or a gentle extension (2nd, 6th, sus4, maj7) over every diatonic chord. There are no minor 2nds, no tritones, no harsh dissonances. The melody is pre-filtered to be safe.
Hearing It in the Song
The Chord Foundation
藍二乗 cycles through the I → vi → IV → V loop in F# major for its entire duration, occasionally substituting ii (G#m) or iii (A#m) for variety. The harmony is deliberately simple because the pentatonic melody provides all the color the song needs. Four chords, five melody notes — the interaction between them creates far more variety than either would alone.
Pentatonic Over a Walking Bass
The verse adds an ascending diatonic bass line under the pentatonic melody:
\[F\sharp \to G\sharp m \to A\sharp m \to B \to C\sharp\]The melody stays pentatonic throughout — the same five notes sound completely different as the chords shift beneath them. Over G#m, D# becomes a 5th; over A#m, it becomes a 4th. The melody doesn’t change, but its harmonic meaning does.
The 5% — Non-Pentatonic Notes
The 5% of notes outside the pentatonic scale are passing tones and chromatic ornaments — brief departures (orange in the player) that add tension before resolving back. They are almost always:
- Chromatic approach notes (a half step below a pentatonic target)
- The diatonic 4th or 7th used as a quick passing tone
- Part of a chromatic run (e.g., the G → G# run over the Outro’s bV chord)
These departures are essential — without them, a purely pentatonic melody would sound static. The 95/5 ratio is the sweet spot: familiar enough to feel natural, varied enough to stay interesting.
Two Non-Diatonic Chords
The song is almost entirely diatonic, with two exceptions (red in the player):
C major (bV) — appears in the Outro, a half step below the dominant C#. Functions as a chromatic approach chord, with the bass walking C → C#.
E#dim / F (vii°) — the leading-tone triad, appearing in the Intro and Chorus 3. Shares two notes with V7 and functions as a dominant substitute.
Why Pentatonic Writing Works
Four properties that make pentatonic melody over diatonic harmony so effective:
1. Zero dissonance risk. The pentatonic scale cannot form a tritone with any diatonic chord tone. The melody can never sound “wrong.”
2. Automatic extensions. Non-chord pentatonic notes become natural extensions — 9ths, 6ths, sus4s — that add richness without tension. The melody decorates the harmony for free.
3. Modal ambiguity. D# minor pentatonic = F# major pentatonic. The melody lives in both the relative major and minor simultaneously, matching the emotional ambiguity of the I → vi → IV → V loop.
4. No half steps. Every pentatonic interval is a whole step or minor 3rd. This makes melodies feel natural and singable, even at 214 BPM with a distorted guitar.