New JGT Lesson: The Cycle of 4ths

In this JGT lesson, jazz guitarist Leon Rodriguez explains the cycle of 4ths by string set in triads

We’ve seen how the notes of a 3-part harmony can be restacked to configure 3 unique voicings, The root position with the root note as the lowest note, the 1st inversion with the 3rd as the lowest note and 2nd inversion with the 5th as the lowest note. There are 3 inversions because there are 3 notes in the triads. 

Let’s select the {654} stringset, which we associate with bass notes, to illustrate how the fretboard presents the cycle of 4ths by alternating our 3 inversions. It goes without saying that we want to transfer these voicing cycles to all 4 stringsets of 3; {654}, {543}, {432} and {321} which are illustrated in Volume 3 – Triads of my series. 

In the example, we see a blue box placed arbitrarily around 3 adjacent triads in this cycle of 4ths. Any 3 adjacent triads in this cycle of 4ths will produce the *primary progression in the key of the center triad. The triad to the right is the 4th of the key and the triad to the left is the 5th of the key producing the I-IV-V progression of the root of the center triad; in this case, the key of A. The voicing here has no relevance to the assignment of the degree of the triad relative to the key. If you slid that blue box anywhere on the cycle, it would be a 1-4-5 progression of the center triad’s key. Again, in this case, A major. Mentally slide it around, and play a little shuffle! Theory! 

The red arrows illustrate the common tone between the adjacent triads in the cycle. I use a little internal sentence to keep that common tone straight. I say, “The root of this is the 5th of the next” as I Proceed down the cycle of 4ths. Works every time. 

This can best be illustrated by visualizing the symmetry of the theory in triads. A simple graph of chromatic as a function of Cycle. We simply spell the triad in columns. 

Don’t be intimidated because you already know this intuitively. We’re just doing deep dive into what you already know to be pleasant to your ear. The common tone has a lot to do with that. 

I use the following graph with my students to illustrate the common tone down the cycle. Red is the Root of the triad because it begins with an R, Blue is the 3rd because the 3rd is so important in the blues and finally Gold is the 5th because it is a structural tone and transfers the power of the allegiance of the tonality. 

One of the most important things we’ve learned since Pythagoras defined the overtone series is that music has a kind of direction it prefers. What Tal Farlow calls the “gravity of music”. It wants to proceed either: 1.) Chromatically, 2.) along the cycle or 3.) scalar. This chart explains why. 

If we will notice the movement (left to right) down the cycle, the common tone changes from the root to 5th, both structural tones, being the same note, makes the change of the function of note seamless. No better voice leading is possible. The 3rd, in blue, is chromatic moment to the root of the next, the next best possible voice leading. 

While all these triads are major, the point is nevertheless made. Even if we adjusted, the 3rds to meet the requirements of a particular key placing whole step between the minor 3rd and the root, the third most preferable movement, scalar motion, is then satisfied! 

I hope my methods don’t disengage anyone. Take my word for it. It all ends up on the fretboard and in your fingers where it belongs. *Since I mentioned the primary progression being targeted for this lesson, I should explain that the secondary progression of a key is all minors and is made up of the ii, iii, and vi of a major key. 

In the key of C major the secondary progression would include A minor, D minor and E minor as the 1-4-5 of the key of A minor. 

To be continued…Books and On-Line Private Lessons available at www.LeonRodriguezGuitar.com/shop 

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