The Complete Guide to Tetrachords

So what is a tetrachord? Four notes — that's all. But those four-note shapes are the biggest labour-saving device in scale learning: master twelve of them and you hold every mode of seven scale families. That's 49 scales, assembled from parts, instead of memorised one at a time.

The word itself means four strings (tetra = four, chord = string) — it relates to the four strings of the ancient Greek lyre, which was tuned to tetrachords. In ancient Greece these four-note cells, built from tones and semitones, were the raw materials of the music that constructed their scales. Quite a pedigree for something a bass player can learn in an afternoon.

Below: how a scale splits in two, the four diatonic shapes that build every mode of the major scale, the eight more that complete the whole system, and how to get it all under your fingers. Prefer it on paper? Both free PDFs are at the bottom ↓

Two halves of a jigsaw

A seven-note scale splits neatly down the middle. Add the octave on top and you're left with two groups of four notes. The lower four form the lower tetrachord; the upper four, ending on the octave, form the upper tetrachord. Together they account for every note in the scale.

Take C major apart and you get C D E F and G A B C. Both halves are the same shape — tone, tone, semitone — joined by a tone from F up to G:

That gap between the 4th and the 5th is the join, and it's worth watching. Across the seven modes of the major scale the join is a tone in five of them and a semitone in the other two — Lydian, whose lower half reaches up to a ♯4, and Locrian, whose 5th is flattened.

One thing to clear up early: despite the name, a tetrachord is not a chord. It's a four-note scale fragment played stepwise, not a stack of thirds — the "chord" in the word is the lyre string, not the guitar chord.

The four diatonic tetrachords

Four shapes — and only these four — account for every half of every mode of the major scale. All are shown rooted on C so you can hear exactly what changes between them. Each one is named after the mode it opens, and each has an older nickname that tells you its character.

1 · The Ionian tetrachord — the major tetrachord

1 · 2 · 3 · 4 — tone, tone, semitone. Bright and settled: the first four notes of a major scale, doh, ray, me, fah. The semitone lands last, at the top. Two of these a tone apart build the major scale itself — it's the most common tetrachord in Western music, and the one your ear treats as home.

2 · The Dorian tetrachord — the minor tetrachord

1 · 2 · ♭3 · 4 — tone, semitone, tone. Minor, but not dark: the ♭3 arrives while the 2 is still natural, so it sounds thoughtful rather than sad. Two of these a tone apart build the Dorian scale, and it's also the lower half of natural minor, harmonic minor and melodic minor — the workhorse of minor-key bass playing.

3 · The Phrygian tetrachord — the Spanish tetrachord

1 · ♭2 · ♭3 · 4 — semitone, tone, tone. The semitone hits immediately: that ♭2 against the root is the flamenco sound, tense and unmistakably Spanish. Move the semitone to the front and you change a tetrachord's character more than any other single edit.

4 · The Lydian tetrachord — the augmented tetrachord

1 · 2 · 3 · ♯4 — three whole tones in a row, no semitone at all. It floats, refusing to resolve, because it ends on the tritone. It's the odd one out in another way too: it spans an augmented 4th rather than a perfect one, so it can never pair with itself — it needs a partner a semitone above to complete the octave.

Note the position of the semitone! Ionian, Dorian and Phrygian each contain exactly one — at the top, in the middle, at the bottom. That single moving part is what separates them. Lydian has none at all, which is why it sounds and behaves differently from the other three.

Every mode of the major scale, assembled

Here's the claim that makes tetrachords worth learning: the seven modes of the major scale are just those four shapes, paired up. No fifth shape is ever needed.

Read the pattern: Ionian, Dorian and Phrygian are each built from two of the same shape. The other four modes mix two different shapes — which is exactly what gives them their character. And the lower-case numerals aren't decoration: they mark the minor-sounding modes (anything whose own 3rd is minor or diminished), so you can spot the minor ones at a glance.

Want Mixolydian without looking it up? Take the Ionian tetrachord, add a tone, add the Dorian tetrachord: C D E F + tone + G A B♭ C. That's the whole scale, built from two shapes you already know — and the ♭7 that defines the dominant sound falls out of the second shape automatically. This works for any mode of any family: name the lower shape, name the join, name the upper shape, and the scale assembles itself.

Beyond the major scale: the other eight shapes

Harmonic minor, melodic minor and harmonic major can't be built from the diatonic four alone — between them they need exactly four more shapes. Add double harmonic major and the two Neapolitan scales and the system closes with a final four. Twelve shapes, seven families, 49 scales.

Three of the new shapes contain an augmented 2nd — a three-semitone leap. That interval is precisely what a raised 7th introduces into a minor scale, and it's why harmonic minor and its relatives sound the way they do. Here's the full set of twelve, every one rooted on C:

A quiet word about shapes 8, 11 and 12: they span a diminished 4th — four semitones, the same distance as a major 3rd — so strictly they stretch the classical definition of a tetrachord. They turn up only in the most chromatic corners of these scales, and you can safely leave them until last.

A worked example: harmonic minor

Natural minor — Aeolian — is Dorian + tone + Phrygian. Raise the 7th and the upper half becomes the Harmonic tetrachord (1 ♭2 3 4) instead: C D E♭ F + tone + G A♭ B C. One shape swapped, and the augmented 2nd appears. That swap is the entire difference between natural and harmonic minor — and once you've heard it as a swapped top half, you'll never need to look either scale up again.

The placement secret

The other thing worth noticing is how consistently these shapes keep the same jobs. The Harmonic tetrachord is the upper half of mode I and the lower half of mode V in every family that uses it. The Dorian ♯4 shape is always the lower half of mode iv and the upper half of mode vii. Learn a shape's placement once and it transfers between families — which is precisely what makes learning and understanding all these scales a far easier task.

Putting it under the fingers

Knowing the table isn't the same as owning the sound. This is the order that works:

1. Learn the four sounds first. Play all four diatonic shapes rooted on the same note, one after another, slowly. Sing the top note. You're training your ear to locate the semitone.
2. Say the shape as you play it. "Tone, tone, semitone." Naming it while your hand does it is what makes it stick.
3. Move one shape through all twelve keys before adding the next. One shape known everywhere beats four shapes known in one position.
4. Assemble, don't recall. Ask for a mode at random and build it: lower shape, join, upper shape. Check yourself against the complete map in the guide.
5. Play the join deliberately. Stop on the 4th, then step to the 5th. Hearing whether that gap is a tone or a semitone tells you which mode you're in faster than counting up from the root.
6. Take it to a tune. Over a dominant chord, play the Ionian tetrachord from the root and the Dorian tetrachord from the 5th. That's Mixolydian — and it's already a bass line.
7. Only then go chromatic. Shapes 5–8 open up every minor-key scale worth knowing; the last four can wait until those are genuinely comfortable.

Both downloads below print nicely: the reference sheet is four pages — all twelve shapes with notation, TAB, steps and fretboard diagrams, plus a master grid to pin above the music stand — and the complete guide is the whole method: every shape as a full teaching card, every mode of all seven families mapped, worked examples and a practice tracker. Have fun experimenting with them and exploring all these different tone worlds!

Tetrachord FAQs

What is a tetrachord in music?

A tetrachord is a group of four stepwise pitches spanning the interval of a 4th — usually perfect, sometimes augmented, occasionally diminished. The first four notes of any major scale form one. Seven-note scales split into two tetrachords, a lower and an upper, which is what makes them such a powerful learning tool.

Is a tetrachord a chord?

No. Despite the name, a tetrachord is a four-note scale fragment played stepwise, not a stack of thirds. The word means "four strings" and relates to the four strings of the ancient Greek lyre, which was tuned to tetrachords.

What are the four tetrachords of the major scale?

The Ionian (1 2 3 4), Dorian (1 2 ♭3 4), Phrygian (1 ♭2 ♭3 4) and Lydian (1 2 3 ♯4) tetrachords. Between them, these four shapes build all seven modes of the major scale — each mode is simply two of them joined by a tone or a semitone.

What are the two tetrachords of the C major scale?

C D E F (the lower tetrachord) and G A B C (the upper tetrachord). Both are the same shape — tone, tone, semitone — separated by the joining tone between F and G.

How many tetrachords are there?

Twelve distinct shapes cover every mode of the seven main scale families — major, harmonic minor, melodic minor, harmonic major, double harmonic major, and Neapolitan major and minor. That's 49 scales from twelve four-note shapes.