The Diagonals of Tension

How fourths tuning makes scale tension visible on the fretboard.

Every scale has tension. Notes that pull, that resolve, that create color. In fourths tuning, that tension organizes itself into two visible diagonal lines. One runs forward like a /, the other runs backward like a \. Once you see them, you can't unsee them. And once you understand what they mean, every scale on the guitar suddenly makes structural sense.

Part 1: The Three Shapes

Before we get to the diagonals, we need to talk about shapes. In fourths tuning, the major scale (and all its modes) can be played with three-notes-per-string (3NPS) using only three distinct finger patterns:

• WW -Whole step, Whole step (e.g., C D E)
• HW -Half step, Whole step (e.g., B C D)
• WH -Whole step, Half step (e.g., A B C)

That's it. Three shapes. They cycle across the strings in a fixed repeating pattern that starts from a run of three WW shapes:

Here's the key insight: which mode you're in depends entirely on where you enter this cycle. Each mode is just a window of 6 consecutive shapes from this sequence. In fourths tuning, the position shifts up one fret at each WW-to-HW boundary. The full rotation:

You don't learn seven modes. You learn three shapes and where you are in the cycle. That's the entire major scale universe on the fretboard.

I first learned this way of thinking about modes from Graham Young at Leeds Guitar Studio - I swear he has a video explaining it somewhere on his channel, but I can't find it. Either way, his teaching shaped how I think about modal geometry on the fretboard.

Part 2: The Forward Diagonal /

Now here's where it gets interesting.

In fourths tuning, every string is 5 semitones apart. A tritone is 6 semitones. So a tritone is always one string up, one fret forward. Visually, that traces a forward slash / across the fretboard. Anywhere. Every time.

The major scale has exactly one tritone: between the 4th and 7th scale degrees. In C major, that's F and B. This single interval is the engine of tonal harmony. It's what makes dominant chords resolve. G7 contains both B and F -and when it moves to Cmaj7, those two notes resolve by half step in opposite directions (B up to C, F down to E). That's the V-I resolution. The most powerful motion in Western music.

The tritone is also why diminished chords feel unstable (B diminished contains both tritone notes), why Lydian sounds bright (#4 is one of the tritone notes), and why Locrian sounds like it wants to collapse (b5 puts the tritone right against the root).

Now think about what this means on the fretboard. In fourths tuning, the single most important tension in Western harmony -the tritone -is a visible / line running diagonally across your strings. Every mode's unique “color note” is defined by its proximity to this diagonal:

• Lydian: the #4 is one of the tritone notes. Maximum brightness.
• Mixolydian: the b7 is the other tritone note. Dominant pull.
• Dorian: the natural 6 sits one step from the tritone. Mellow tension.
• Locrian: the b5 puts the tritone against the root. Total instability.

The spicy modes get their flavor from proximity to this diagonal. And in fourths tuning, you can feel it under your fingers. The tension literally runs in a line.

Part 3: The Missing Triad

There are four types of triads in Western music: major, minor, diminished, and augmented. The major scale contains three of them:

• Major triads: I, IV, V
• Minor triads: ii, iii, vi
• Diminished triads: vii°

The fourth type, augmented, is completely absent. Zero augmented triads in the major scale. This isn't a coincidence. It's structural.

An augmented triad is built from stacked major thirds: C-E-G#. A major third is 4 semitones. In fourths tuning (where every string is 5 semitones), a major third is one string up, one fret back. That traces a backslash \ across the fretboard.

So the augmented triad is the missing diagonal. The major scale has / but not \. It has tritone tension but no augmented tension. This is why it sounds stable, resolved, “home.” It only pulls in one direction.

Part 4: The Fourth Shape

Remember our three 3NPS shapes? WW, HW, WH. Every note in the major scale fits cleanly into three-notes-per-string using just those patterns. Life is simple.

Now watch what happens when you add an augmented triad to a scale. The three major-scale shapes can't handle it anymore. You need a fourth pattern:

This isn't some obscure edge case. This single additional shape unlocks three scale families that define modern harmony:

Melodic Minor (Jazz Minor)

Raise the 7th of natural minor. This is the backbone of jazz improvisation. Its modes include the altered scale (the go-to sound over dominant chords in jazz), lydian dominant (Mixolydian with a #4 -bright and floating), and lydian augmented. Every serious jazz player lives in melodic minor.

Harmonic Minor

That “exotic” sound -Middle Eastern, classical, flamenco. The augmented second interval between the b6 and natural 7 creates its distinctive pull. Its modes include phrygian dominant (the “Spanish” sound) and the mysterious locrian natural 6.

Harmonic Major

The least explored of the three. Lower the 6th of the major scale. Produces hauntingly beautiful sounds -familiar enough to feel tonal, but with an unexpected darkness. Modes like lydian augmented #2 live here.

What do these three families have in common? Each one contains at least one augmented triad. Each one introduces the \ diagonal onto the fretboard. And each one requires the fourth shape (HWH) in its 3NPS fingering.

The practical takeaway: if you're fluent with the 3 major-scale shapes and want to access the entire melodic minor / harmonic minor / harmonic major universe, you add one shape. That's it. One shape, and the whole landscape of jazz and classical harmony opens up.

Part 5: Both Diagonals Together

Let's put it all together.

The major scale has one diagonal: /. One tritone. Tension runs in a single direction. This is why it sounds clean, resolved, directional. There's a pull, but it's simple.

Melodic minor, harmonic minor, and harmonic major have both diagonals: / and \. Tension runs in two directions simultaneously. This is literally why these scales sound more complex -there is more geometric tension in the note relationships. The notes don't just pull toward resolution; they pull in competing directions.

You can see it and feel it under your fingers. When you're improvising and you want more tension, move toward a diagonal. When you want resolution, move away. The fretboard becomes a map of harmonic pull.

Part 6: The Whole Tone Diamond

There's one more scale that deserves attention, because it takes everything we've discussed and cranks it to the extreme.

The whole tone scale is six notes, each a whole step apart: C-D-E-F#-G#-A#. No half steps anywhere. It sounds floaty, unresolved, dreamlike -Debussy's favorite toy.

Here's the geometric insight: the whole tone scale is just two augmented triads superimposed. C-E-G# is one augmented triad. D-F#-A# is the other. Stack them together and you get all six notes of the whole tone scale. Nothing else.

On the fretboard in fourths tuning, each augmented triad traces a \ diagonal. Two augmented triads means two \ diagonals running in parallel. But the whole tone scale also contains tritones (C-F#, D-G#, E-A#) - so the / diagonals are there too.

The result? Both diagonals, everywhere, crossing each other to form two recurring shapes across the fretboard:

• The Diamond ◇ - four notes where the diagonals form a closed shape, two sideways chevrons joined at their far ends.
• The X ✕ - where both diagonals cross through a single note, two chevrons joined at their points. That center note is simultaneously part of a tritone and a major third relationship.

Together, the diamonds and X's tile the entire fretboard in a repeating lattice:

Every note in the whole tone scale sits on a diagonal. Every note is part of a tritone and an augmented triad. Tension in every direction, at every position. This is why the whole tone scale feels like it has no gravity - there's no resolution because tension is perfectly uniform. The diamonds and X's are the visual proof.

Compare this to the major scale, which has a single / diagonal and no \ at all. The major scale is a highway with one direction of pull. The whole tone scale is a lattice where everything pulls equally on everything else. And in fourths tuning, you can literally see the difference.

Bonus: The Bebop Connection

Here's a fun one. The jazz major scales, sometimes called Barry Harris 6th diminished scales, add chromatic passing tones to the major scale. The major bebop scale (add b6) introduces one note that creates a \ backwards diagonal, effectively shoe-horning in an augmented triad that doesn't exist in the plain major scale.

The jazz major b3 b6 scale goes further, adding two chromatic tones. This introduces two backwards diagonals from two augmented triads. On the fretboard in fourths, you can see these extra diagonals appear as you add each note.

Exercise left to the reader: how do b3 and b6 relate to the whole tone scale? (Hint: look at which augmented triads they belong to, and compare to the two augmented triads that make up the whole tone scale.)

The Framework

Let me boil this whole article down to its essence:

Four shapes. Two diagonals. Every common scale in Western music.

The fretboard stops being a grid of memorized positions and becomes a geometric map of how music actually works. You see the tension. You feel the diagonals. And once you do, the entire fretboard makes a kind of sense that's hard to go back from.