I IV V Rule – Music is Numbers

Let’s make sense of what we already know.

A musical phrase that you will become familiar with is the term chord progression. A chord progression is simply combining a series of chords into a specific harmonious order to accomplish a purpose.

In our first lesson we learned to play the chords in a sequence. We will now arrange these 7 chords into a natural chord progression. This raises some questions. First – What do you mean by a natural chord progression? Second – How do we do this? Third – Why do we to do this? Let’s jump ahead a few months from now into the future. Not knowing the answers to our 3 question could put you in this situation. Imagine Joe the guitar player getting together with friends to play some music. The conversation might sound something like this:
playing in the band

“Let’s play some Blues”. “What Key?” The bass player says “Let’s play it in A.” Everyone says “Okay, Key of A.” Joe wants to join in, but has this look of uncertainty and hesitates. The bass player picks up on this, and says “That’s A D E.” Joe sighs in relief because he knows these chords and says “Oh,,, okay” so he joins inThey have just finished jamming in the Key of A and the singer asks “Hey Joe, do you know (such and such)?” Joe says, “Yeah.” The singer says “Great, play it in G.” Joe says “Uh…….I only know it starting from the C chord….”

This is an uncomfortable situation that many guitar players like Joe have found themselves in, but one that is easily resolved. How is this possible? Having a solid foundation of music and how it all fits together. From this foundation we can continue to build and progress. How will this information help us in Joe’s case and answer our What, How and Why questions?

First – What is music? The American Heritage Dictionary defines music as: “The art of arranging sounds in time so as to produce a continuous, unified, and evocative composition, as through melody, harmony, rhythm, and timbre”. Wow …. That may be true. But it is still too complicated to digest.

Music is Numbers

When we here a musical note it is called a frequency or tone. The high E string on the guitar is tuned to 329.6 Hz (hertz). This means when you pluck the E string it vibrates back and forth 329.6 cycles or times per second producing the sound you hear. The other strings also produce their own tone. For example open the lid of a piano and examine the sound board and strings. They range from long thick strings to short skinny strings. If you were to run your finger across them you will here the different tones or frequencies each string produces, from very low to very high sounds.

Music can be played with a complex instrument such as an electronic keyboard or a simple object like a rubber band. Pluck it as you stretch if back and forth and you can create music. Your voice is also an instrument that can play one note at a time. As you exhale, the air from your lungs passes through your larynx or voice box. Inside the voice box are two tiny folds of muscle call vocal chords. When you sing a song or hum notes you are either tightening or loosening your vocal chords to produce the desired sound..

A chord is a combination of musical notes that mathematically and harmonically combine to produce a sound that is pleasant to the ear. What we mean by this is – when we play a chord or a combination of chords, the frequencies or notes produced have to mathematically fit together. For a visual idea of how it works…take your hands and hold them out in front of you and spread your fingers. Now bring your hands together so the fingers interlock with each other. That’s how music works. Even though each note is producing a different vibration, the numbers have to mathematically combine or fit together.

Again for visual effect, take your hands as before and spread your fingers apart. Now, as you bring your finger together match finger tip to finger tip and push. What is the affect? You feel resistance. If the notes or frequencies do not mathematically combine they push against each other and produce what is called a sour note. This is why, we could have a 1000 violins playing harmoniously together or a group of 3 or 4 musicians playing together and if one player plays a note or chord that does not harmonically combine with the other notes or chords you will hear the sour note as plain as day. Why? Because it clashes and does not mathematically fit.

Music is numbers. These are the frequencies of the guitar’s open strings.


With this understanding as our base foundation we can now answer the question – How do we know what chords naturally go together?

The answer: The I IV V Rule or method. This is a simple method, for what ever reason naturally combines chords that are pleasing to the ear. Applying this simple rule allows us to arrange the 7 Basic chords into 5 Keys or a combination of chords that work together musically. This method is the first step in understanding music composition.