CIRCLE OF FOURTHS The Essential System
Simon Troup explains how the Cycle of 4ths is a powerful songwriting tool and also a great chord progrssion for improvising over.
The circle of 4ths is a variation on a concept known as the circle of 5ths. These conepts are closely related since a 4th is essentially an inverted 5th; but the circle of 4ths creates a specific style of composition, and it’s this that we are focusing on here.
The ‘circle’ is the visual representation of a progression of diatonic chords that can be heard in numerous styles of music. Good musicians recognise these patterns just as they recognise a 12-bar blues. Knowing how to handle such changes, and to embellish and improvise over them, is necessary if you want to be a versatile musician. You’ll find these progressions in the music of Bach, Bacharach and The Beatles, and as easy to find in jazz as in Judas Priest songs - which should tell you something about their universal appeal.
The building blocks of these progressions are the diatonic chord families of the major and minor scales - ie sets of chords built using scale tones only - as either triads or 7th chords. Most people’s first experience of this is learning the sequence ‘major minor minor, major major minor’, representing the pattern of chords in a major key, I through VIm. Therefore our first few examples demonstrate different ideas using this harmonised chord scale.
The diagram (Fig 1) opposite shows the diatonic circle of 4ths in the key of C (C D E F G A B) as a series of 7th chords: Cmaj7-Fmaj7Bm7b5-Em7-Am7-Dm7-G7-Cmaj7. These are on the outer ring. The inner ring is a Roman numeral system from I to VII, the numerals tallying with the outer circle chords (I=Cmaj7, IV=Fmaj7 etc) and smaller numerals filling in the gaps between the 4th chords.
Once you have understood this diagram, it is worthwhile to do the same in other keys. At first you could focus first on guitar friendly keys such as D major (D E F# G A B C#), G major (G A B C D E F#), A major (A B C# D E F# G#) and E major (E F# G# A B C# D#).
Fig 2 shows the diatonic chord family of C major with each chord being a 7th of some kind (maj7, m7, 7 and m7b5). Again, get to know the 7th chords in every key.
Fig 3 shows how secondary dominants can be applied to each chord in the major scale (here, C major). A secondary dominant is a dominant 7th chord that resolves to another chord in a scale other than the tonic (the C of C major), making a smooth transition from one chord to another. While, say, Cmaj7-Dm7 is a great chord progression the Dm7 won’t sound resolved until it’s prepared for properly. By adding A7 in front of Dm (or Dm7) the change is more resolved, as if you’ve moved away from C to be in Dm. Secondary dominants can prove very useful in a circle of 4ths scenario; Cmaj7-Fmaj7 can be elaborated on with Cmaj7-C7-Fmaj7 (Fmaj7 sounds more settled now) or similarly, Am7-Dm7 can be enhanced as Am7-A7-Dm7.
With these three diagrams understood (and ideally explored by you, sooner or later), you’re now ready to tackle the examples that follow. You’ll go from chord primers that harmonise the C major scale to playing chord progressions in circles of 4ths then onto using secondary dominants. After this, you’ll explore the same terrain using arpeggios. Happy circling!