Updated: Oct 29, 2019
Just as DNA is made up of the building blocks (nucleotides) that tell cells how to make up organisms, there are building blocks that make up the scales we use in music. Music starts with individual notes that are strung together like DNA into groups that create musical "chords" or lines. Don't let the term "chord" confuse you, chord comes from the Greek χορδά (khordá) which literally means string. Originally, when musicians talked about chords, they were referring to the number of strings that their zither (harp) had. A group of two notes is called a duochord (or an interval). A group of three notes is called a trichord. Four notes form a tetrachord. Five, a pentachord (or pentatonic scale). Six, a hexachord (or hexatonic scale), and seven is a heptachord (or heptatonic scale). Our Western Major and Minor scales fall into this last category. There are others, but that's enough for now. For today, we are focusing on creating melodies with tetrachords.
For this lesson, some previous knowledge of scales, intervals, and musical steps is very helpful. If musical steps are new to you, you can visualize a piano keyboard or a guitar where a half step is two frets on the same string or pIano keys that are right next to one another and a whole step has one fret or key between it. For example, A to B is a whole step and A to B♭is a half step.
A tetrachord is a series of four notes; the interval between the first and last notes spans no further than a tritone or six-half steps.
A tetrachord is a series of four notes; the interval between the first and last notes spans no further than a tritone or six-half steps. Tetrachords can be thought of as making up half a Western scale. Two tetrachords can be strung together to form an eight-note-long major or minor scale. When two tetrachords are linked together to create a scale, they are referred to as "Tetrachord I" and "Tetrachord II" respectively. Though there are many variations of tetrachords that can be built. First, we will focus on how tetrachords are used to build Western major and minor scales. Then we will complete a melody building activity using tetrachords. Lastly, we will discuss some other common tetrachords that you can add to your music practice.
Tetrachords may be an unfamiliar concept to even some experienced musicians. I was unaware of them until I studied guitar even though I had studied piano and voice for years previously. However, they are a common topic that guitarists and bassists to study because understanding them facilitates improvisation skills and the patterns they form fit well under a guitarist or bassist's fingers. Such string players often start their improvisation studies with tetrachords. But, they are for more than just guitar and bass players as they make a great building block for improvising, composing, and technical practice for all instruments and even the voice. All musicians will benefit from creating their own warm-ups with tetrachords and flexing their improvisational muscles.
Building Major and Minor Scales with Tetrachords
As we mentioned before, Western major and Minor Scales are built of tetrachords. When two tetrachords are linked together to create a scale, they are referred to as "Tetrachord I" and "Tetrachord II" respectively. The graphic below shows the tetrachords that make up major and minor scales starting on the pitch "C." To build other major and minor scales, you would take the same half and whole step patterns as though shown below but start them on the desired pitch.
The Major Tetrachord
The first type of tetrachord is the major tetrachord. A major tetrachord is built of a whole step, followed by another whole step, followed by a half step. Two major tetrachords placed in succession forms a major scale. For example, in C major, Tetrachord I is built with the notes C, D, E, and F. As C to D is a whole step, D to E is another whole step and E to F is a half step. While Tetrachord II is built with the notes G, A, B, and C. As G to A is a whole step, A to B is another whole step and B to C is a half step.
A major tetrachord is built of a whole step, followed by another whole step, followed by a half step.
Tetrachords and Minor Scales
While a major scale is formed with two major tetrachords, minor scales are formed of two different tetrachords. We will discuss the three types of minor: natural, harmonic, and melodic one at a time.
In natural minor, Tetrachord I is a minor tetrachord. It is sometimes referred to as a Dorian tetrachord. A minor tetrachord is built with a whole step, followed by a half step, followed by a whole step. In C natural minor, Tetrachord I is built with the notes C, D, E♭ , and F. As C to D is a whole step, D to E♭ is a half step and E♭ to F is a whole step
A minor (or Dorian) tetrachord is built with a whole step, followed by a half step, followed by a whole step.
In natural minor, Tetrachord II is an upper minor tetrachord. It is also sometimes referred to as a Phrygian tetrachord as it forms the first part of then Phrygian mode in the medieval church mode system. (Don't worry if you are not familiar with medieval church modes; we will discuss modes in another post.) The upper minor (or Phrygian) tetrachord is built with a half step, followed by a whole step, followed by a whole step. In C natural minor, Tetrachord II is built with the notes G, A♭, B♭ , and C. As G to A♭ is a half step, A♭to B♭ is a whole step and B♭ to C is a whole step.
The upper minor (or Phrygian) tetrachord is built with a half step, followed by a whole step, followed by a whole step.
In harmonic minor, Tetrachord I is a minor chord just like in natural minor. However, Tetrachord II is a harmonic tetrachord. It is sometimes called a "Hungarian Minor" or "Gypsy Minor" tetrachord. A harmonic tetrachord is built of a half step, followed by a whole+half step (or 1½ step), followed by a half step. The whole+half step (or 1½ step or three half steps) sounds like a minor third though it is musically spelled differently. In C harmonic minor, Tetrachord II is built with the notes G, A♭, B, and C. As G to A♭ is a half step, A♭to B is a whole+half (1½ step) and B to C is a half step.
A harmonic tetrachord is built of a half step, followed by a whole+half step (or 1½ step), followed by a half step.
In ascending melodic minor, Tetrachord I is again a minor tetrachord. While Tetrachord II is a major tetrachord. This means that in C melodic minor ascending, Tetrachord I is the same as it is in natural and harmonic minors and Tetrachord II is the same as it is in C major. Since a descending melodic minor scale is the same as a descending natural minor scale, Tetrachord II is an upper minor (or Phrygian) tetrachord and Tetrachord I is minor, just as it is in natural minor.
Melody Building Exercise
For this exercise, you can either play along with the provided chord progression or you can accompany yourself if you play a harmonic instrument.
1. Starting with the C major Tetrachord I, play through the four notes up and down stepwise several times getting used to how they feel in your hands or voice and how they sound without accompaniment. Employ a variety of rhythmic patterns, meters, and tempos.
2. Now experiment playing with these same notes only C, D, E, F but add skips and steps. Again, experiment with different rhythmic patterns, meters, and tempos. Have fun with it! You should start to hear that what you are playing is beginning to sound like a melody.
3. This time, continue to experiment with the major Tetrachord I in C major but add the accompanying chord progression in common time. (Or, play along with the pop ballad version of the chord progression in the video above.)
𝄆C |C |Am |F |C |C |Dm |G 𝄇C 𝄂*
*C major is C, E, G.
Am is A, C, E.
F is F, A, C.
Dm is D, F, A.
G is G, B, D.
Repeat this pattern as many times as you like. Ending after the last G major chord on a C major chord. See how different notes from the C major Tetrachord I sound against the harmony. Which pitches are dissonant? Which are consonant?
4. Now repeat the exercise but play the C major Tetrachord II. Then add other C-pitch tetrachords as well. Mix and match. For example, play the C major Tetrachord II over the Dm and G measures. Or, play the the C minor Tetrachord I over the Am and F measures. Listen to how what types of sounds you experience. How do these over tetrachords fit with the harmonies? Do they fit with some and not others?
Beyond Major and Minor – Other Tetrachords
Blues and Jazz musicians (and others) often improvise using tetrachords other than those that make up Western major and minor scales. Try out the following tetrachords with the 12-bar Blues Tetrachord chord progression in C either with the audio sample in the video below or by accompanying yourself.
The 12-Bar Blues in C
𝄆C7* |C7 |C7 |C7 |F7 |F7 |C7 |C7 |G7 |F7 |C7 𝄇*
*In this Blues progression, all of the seventh chords are dominant seven chords.
C7 is C, E, G, B♭
F7 is F, A, C, E♭
G7 is G, B, D, F
Whole-Tone (sometimes referred to as lydian) tetrachord
Whole Step - Whole Step - Whole Step
example: C to D D to E E to F♯