Music TheoryChordsHarmony

What Is A Tetrachord In Music?

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Written by Samuel Chase

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In music, chords are the main building blocks of harmony and songs in general. There are many different kinds of chords, and each has a different harmonic function and reason why they work in the music.

In this post, we will be defining what a tetrachord is, how it’s used in music, and how to create one. To help us do this, we first need to define what a chord is. 

What is a Chord? 

Whenever you play or sing more than one note simultaneously, you are producing a chord.

A chord can have any number of simultaneous notes (as long as it’s more than one), and chords with different numbers of notes are called different names.

A chord with two notes is called an interval or a dyad, and a chord with three notes is called a triad

Triads are the most common chord you find in music, and whenever you see a chord written with just a note – for example, C chord or F# chord – it signifies a major triad chord.

There are chords with more than three notes, like Sixth chords, Seventh chords, added tone chords, and extended chords

Chords are generally built from scales, which are groups of notes sorted by pitch in either ascending or descending order.

For example, you most likely have seen this picture, which is a C Major scale: 

C major scale

Now, from this scale you can make a C Major triad by taking the first (called the root), third, and fifth notes – C, E, and G. 

What is a Tetrachord? 

A tetrachord is unique among musical terms with the word “chord” in them, because it actually is technically not a chord as defined above.

In fact, it is closer to a scale, because it is a series of notes played one at a time.

In Greek, the word “tetra” means four, so therefore a tetrachord is a series of four notes, with the extra specification that the four notes are taken from a span of five semitones, or half steps

A semitone/half step is the smallest interval in Western music.

There are 12 semitones in an octave interval, as shown in the chromatic scale.

A whole tone is simply an interval of two semitones:

Chromatic scale

A span of 5 semitones is the same as a Perfect 4th interval.

C ⇨ F or G ⇨ C are examples of Perfect 4ths.

Therefore, an example of a tetrachord could be four notes spanning C ⇨ F or G ⇨ C.

All tetrachords have three intervals (in between the four notes) and these intervals are almost always either a semitone or a whole tone:

C – F tetrachord and G – C tetrachord

History and Uses of Tetrachords

The first people to use tetrachords and develop music theory from them were the Ancient Greeks.

They developed three types of tetrachords – diatonic, chromatic, and enharmonic.

Diatonic Tetrachords

In a diatonic tetrachord, the three intervals used are two whole tones and one semitone.

An example would be a Major or minor tetrachord (e.g. C – D – E – F or A – B – C – D).

C – F (Major tetrachord) and A – D (minor tetrachord)

Chromatic Tetrachords

In a chromatic tetrachord, there is one interval that is a minor third, and two semitone intervals.

This is a rare example of a tetrachord with an interval greater than a whole tone.

An example would be D – E#(F) – F# – G. 

Chromatic tetrachords

Enharmonic Tertrachords

An enharmonic tetrachord is one you’re likely to never see used.

It has one interval of a major third (four semitones) and then two intervals of half a semitone.

Because this involves microtonal notes (e.g. B half-sharp), it is hard to notate and even harder to play.

Use of Tetrachords by The Greeks

The Greeks had specific names for the four notes of a tetrachord.

In ascending order they were:

  • hypate
  • parhypate
  • lichanos
  • mese

While these terms aren’t widely used today, you still might see them sometimes when identifying notes in a tetrachord:

Greek names of tetrachord notes

Use in Classical Music 

In the Classical and Romantic Era, tetrachords were based upon equal temperament, and were used to explain many types of scales, like major and minor: 

The Major tetrachord uses the interval pattern tone – tone – semitone (e.g. C – D – E – F). 

The minor tetrachord uses the interval pattern tone – semitone – tone (e.g. C – D – Eb – F). 

The harmonic tetrachord uses the interval pattern semitone – minor third – semitone (e.g. C – Db – E – F). 

The upper minor tetrachord uses the interval pattern semitone – tone – tone (e.g. C – Db – Eb – F).

Qualities of tetrachords

To make the average scale that we use in modern music, all you have to do is stack these tetrachords on top of each other, putting the second (top) one a whole tone above the end of the first one – for example, a Major C – D – E – F plus another Major tetrachord G – A – B – C makes up a C Major scale.

The second tetrachord starts on G, which is a whole tone above the F at the end of the first tetrachord. 

Tetrachord StackIntervals (T = tone, S = semitone, m3 = minor 3rd)Scale
Major + MajorT-T-S : T : T-T-SMajor
Minor + Upper MinorT-S-T : T : S-T-TNatural Minor
Major + HarmonicT-T-S : T : S-m3-SHarmonic Major
Minor + HarmonicT-S-T : T : S-m3-SHarmonic Minor
Harmonic + Harmonic S-m3-S : T : S-m3-SDouble Harmonic/Gypsy Scale
Major + Upper MinorT-T-S : T : S-T-TMelodic Major
Minor + MajorT-S-T : T : T-T-SMelodic Minor
Upper Minor + HarmonicS-T-T : T : S-m3-SNeapolitan Minor

Summing Up – Tetrachords

Tetrachords are a unique brand of chord because they aren’t multiple notes being played at once.

In fact, they act more like scales, and can be combined to make many different types of scales.

Overall, tetrachords are rare and aren’t often mentioned by name in music theory, but they have a strong influence on melody and harmony writing, so it’s helpful to be aware of them.

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Samuel Chase has been playing music since he was 5 years old, and teaching music since he was 13. He has a PhD in Music from the University of Surrey, and he has composed music that has been played in three different countries. He is currently working as a film composer and writing a book on film music.