The Harmonic sequence is a sequence of chords relating to a specific scale, built according to the specific theoretical rules. It is frequently used in modern music, pop, rock, country, and jazz. Almost all musical types can use this system. With harmonic instruments like the piano, the keyboards and the guitar, it is often used as a learning tool.
For example, it's a useful system for learning the chords in all the scales. But it can also be used to study and experiment with improvisation. In fact, you can find a section devoted to improvisation in the harmonic sequence.
A harmonic sequence is built on one scale using four chords relating to four degrees of that scale. We will clarify this concept shortly, using an example in C major.
Look at the sequence of degrees of the C major scale.
| I | II | III | IV | V | VI | VII | VIII | |||||||
| C | D | E | F | G | A | B | C |
The rules that define the construction of the chords, analyzed in the triads section, allows us to establish how chords inherent to a specific scale can be extracted from a sequence of notes. In the example, which is in C major, the chords related to the C scale are the following:
| I | II | III | IV | V | VI | VII | VIII | |||||||
| C | Dm | Em | F | G | Am | Bdim | C |
The harmonic sequence requires the use of four chords related to the same scale of the sequence. Here are the chords that come from the I°, VI°, II° and V° degrees of the major scale, and are usually played in the order seen below. In the scale of C we therefore have:
You may have noticed how the G is played as G7. Usually the V° degree of the scale is played as the "seventh", while the I° is major and the II° and VI° are minor.
The system is quite simple. To verify that you have really understood it, lets look at another scale, A major for example, where we can look at the harmonic construction of its triads.
| I | II | III | IV | V | VI | VII | VIII | |||||||
| A | Bm | C#m | D | E | F#m | G#dim | A |
We use the same procedure as before, in order to play the chords put on the I°, VI°, II° and V° degrees of the major scale, played in the order seen below. In the A scale, we therefore have:
Remember that the V° step is always played as "seventh."
Therefore, to make a harmonic sequence is simple. In the following chart you can see the harmonic sequences of all the scales.
| Scale | I° | VI° | II° | V° |
| C major | C | Am | Dm | G7 |
| G major | G | Em | Am | D7 |
| D major | D | Bm | Em | A7 |
| A major | A | F#m | Bm | E7 |
| E major | E | C#m | F#m | B7 |
| B major | B | G#m | C#m | F#7 |
| F# major | F# | D#m | G#m | C#7 |
| C# major | C# | A#m | D#m | G#7 |
| G# major | G# | E#m | A#m | D#7 |
| D# major | D# | B#m | E#m | A#7 |
| A# major | A# | F##m | B#m | E#7 |
| F major | F | Dm | Gm | C7 |
| Bb major | Bb | Gm | Cm | F7 |
| Eb major | Eb | Cm | Fm | Bb7 |
| Ab major | Ab | Fm | Bbm | Eb7 |
| Db major | Db | Bbm | Ebm | Ab7 |
| Gb major | Gb | Ebm | Abm | Db7 |
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