I came into this article thinking I basically had all the knowledge ready to go. But I discovered something new about the I IV V chord progression that helped me understand why it’s such a powerful progression in tonal music.

In tonal music the I IV V chord progression is a sequence of chords based on the 1st, 4th, and 5th scales degrees. For example, in the key of C major the progression would be (I) C-major, (IV) F-major, and (V) G-major.

In this article I’ll go over the basics of the I IV V progression but I’ll also reveal an interesting insight into why this progression is so dominant in tonal music.

I IV V – Prerequisites

In order to follow the discussion it’s necessary to understand the following concepts:

• Key Signature
• Scale Degrees
• Triad
• Major and Minor Chords
• Inversions
• Roman Numerals

What is a musical key signature?

The key signature is what indicates how many sharps or flats are used in the piece of music. Key signatures can change throughout the piece. Also, music typically includes accidentals (notes outside the key signature). For this article I’ll be using C major for most of my examples. C major has no sharps and no flats.

What is a scale degree?

A scale degree is a numeric identifier for each pitch in a scale. In a diatonic scale, like C major, there’re seven scale degrees – one for each pitch.

What is a triad?

A triad is a combination of three pitches played at the same time. Chords are built from triads. Here are some examples of triads.

What are major and minor chords?

Major and minor chords are triads with a specific set of intervals. A major chord consists of a major 3rd (4 half-steps) from the bottom note and a minor 3rd (3 half-steps) up from that note. A minor chord consists of a minor 3rd (3 half-steps) up from the bottom note and a major 3rd (4 half-steps) up from that note.

Major and minor chords are triads because they have three pitches. The three pitches have names: the root, the 3rd, and the 5th.

What are inversions?

Inversions are how we label chords so we know which note is in the bass (the lowest note of the chord). In a triad there are 3 positions and 2 inversions. Inversions are determined by identifying the intervals up from the bass note when the notes are brought within an octave range. There is root position where the notes are stacked up in thirds. There’s 1st inversion where you get the intervals of a 6th and a 3rd. Lastly, there’s 2nd inversion where you get the intervals of a 6th and a 4th.

What are Roman numerals?

Roman numerals are a method of music analysis that highlights the harmonic function of chords typically within a tonal system. Each scale degree gets a corresponding Roman numeral. Each Roman number gets another name that is used to identify it. I have written more about Roman numeral analysis in this article: Music theory and math

This is where we get the I IV V notation from!

Three reasons why the I IV V progression is so dominant in tonal music

I’m sure there’re many reasons this progression has maintained such a hold on tonal music but the three I’ll cover are: bass movement, home away more away home, and strong establishment of the key.

I IV V bass movement

In the key of C major, when in root position, the I IV V I bass movement is C –> F –> G –> C. The intervals are C to F = P4th/P5th, F to G = M2nd, G to C = P4th/P5th. With this we get two strong bass movements of a P4th/P5th. These are strong motions because the interval of a Perfect 5th is infused in the tonal system stemming from the overtone series.

The second measure achieves nice upward stepwise motion leading back to the tonic (I).

Home away more away home

In tonal music, the “story” of the music is typically one of home – away – home. Or tonic – dominant – tonic. In tonal music there is a sense of return there’s a feeling of “progression.” Not all music moves in this manner – it’s not a given. In the I IV V progression we get an extra step added in between the I V progression. The IV is like a bridge between the tonic (I) and the dominant (V). One way that the IV acts like a bridge is by having a common tone with the tonic: CEG (I) and FAC (IV). Another common tone bridge can exist if you add a 7th to the V chord: GBDF (V7). Now you have a connection of common tones going from the I to the IV to the V7 and back to I. Then from the IV to V the IV chord can move by step-wise motion or a leap of a P4th/P5th.

Also, all three chords are major. That means you don’t get a “jarring” shift from major to minor. The common tones along with stepwise or P4th/P5th bass movement all contribute to this progression’s power. There are other chords that can yield similar results but you will have to make some sort of compromise. The I IV V progression stays close enough to tonic while exploring far enough away to give some variety. It’s comfortable.

Strong establishment of key

This one is the characteristic of the progression that I had never thought of. I was reading Structural Functions of Harmony by Arnold Schoenberg and he points out that this progression rules out other closely related keys that the piece of music could be in. When we first begin to hear a piece of music our ears are searching for patterns. If you are acclimated to tonal music, then you are unknowingly listening for very specific relationships. Let’s just take the four chord progression below. The first chord you hear is a C major chord. You don’t know what key the music is in at this point because you have only heard three pitches. The next chord, FAC (IV), gives you two more new pitches. And more importantly it gives you F natural. This F natural is important because it rules out the possibility of the music proceeding in the closely related key of G major. G major’s key signature has one sharp – an F sharp. The next chord is GBD which completes the tonal picture by providing two critical pitches. The addition of pitches B and D complete the C major scale if we combine all the notes from the I and IV.

Chord	Pitches
C major	C E G
F major	F A C
G major	G B D

With these three chords we have introduced all seven pitches of the key (C D E F G A B). The second way the V chord establishes the key is with the B natural. The B natural rules out the option of the piece continuing in F major. F major is closely related to C major. F major just has a B-flat in the key signature. Because we hear a B natural we know it’s not in F major.

By going through these three chords we get the sound of the tonic, get all the pitches of the key, and rule out the possibility of the music being in either of the closely related keys! This progression plants the listener firmly in the desired key. Other progressions can complete this task. For example: I ii V I or I ii vii I. But these progressions have changes in chord quality from major to minor, which is not quite as smooth as the I IV V.