In this lesson, we will learn to play the diatonic chords of the major scale in a special sequence: Diatonic Fourths.
This is a very special relationship found in harmony which you really want to know.
First, What Are Fourths?
You'll remember from previous lessons (basic intervals) that fourths are intervals.
An interval is the distance between two notes. That is, how many half-steps lie between a pair of notes.
All of the intervals have names like minor 2nd (1 half-step), major 2nd (2 half-steps), minor 3rd (3 half-steps), major 3rd (4 half-steps), and...
Perfect 4th (5 half-steps), and...
Augmented 4th (6 half-steps).
If you've forgotten the intervals, go back and review. They're essential. For this lesson, you mainly need to know that an ascending perfect fourth is 5 half-steps, and an ascending augmented fourth is 6 half-steps.
What Are Diatonic Fourths?
Diatonic fourths are intervals of a fourth found in the scale. That is, notes in the scale which are 5 or 6 half-steps apart.
For instance, in the key of G from the note G ascending to C is 5 half-steps—a perfect fourth.
Or, from the 4th of the G major scale (C) ascending to the 7th of the G scale (F#) is 6 half-steps—an augmented fourth.
Diatonic fourths are fourths occurring in the key. In the major scale they're all perfect 4ths except for one augmented fourth between the 4th degree of the scale and the 7th degree.
The Major Scale in Diatonic Fourths
We can play all seven notes of the major scale in diatonic fourths forming a loop.
This would go: Root - 4th - 7th - 3rd - 6th - 2nd - 5th - Root...
Each note is 5 or 6 half-steps above the previous note.
In the key of G this would be: G – C – F# - B – E – A – D – G
So we're not jumping all over the fretboard, we will sometimes drop down an octave instead of going up every time. Regardless of octave, we still regard the sequence as “moving in fourths.”
Play the animation to see and hear the G major scale in 4ths:
Diatonic Chords in Diatonic Fourths
Just as we can play the notes of the major scale in diatonic fourths, we can play the diatonic chords of the major scale in diatonic fourths.
The diatonic chords in diatonic fourths would go:
I – IV – vii – iii – vi – ii – V – I
It's the same loop, but playing the chord instead of just the roots of the chords.
When chords move in ascending fourths, it is often called a cycle progression, or circle progression since it moves around the circle of 5ths and 4ths. (You might recall I already set you up for this concept with the fretboard note naming exercises. I've taught you all sorts of things you don't even realize yet!)
Why You Should Practice Chords in Fourths
This sequence of chords contains many of music's most common chord progressions and chord movements.
We recently discussed that what makes a chord progression work well is that it takes you on a journey. Chords moving in fourths are one of music's strongest journeys. These progressions aren't accidents; they sound good. And, that's why people keep using them.
Chords don't always move this way, but they like to. This series wants to bring you back to the I chord.
If you work backwards through this series of chords, it reveals many common chord progressions.
Let's look at these progressions on the next page...