The I-IV-V chord progression is one of the cornerstones of Western music, uniting everything from Mozart to Missy Elliott. Bob Marley’s “Stir It Up” is as clear and concise an introduction to I-IV-V as you could ask for.
The song uses three chords: A, D, and E. They’re shown in the diagram below as turquoise, blue, and pink lines respectively.
The “Stir It Up” riff is two bars long. The first bar spells out a slightly ornamented A chord. The second bar spells out the D and E chords.
Let’s look at the two bars in more detail. The first bar starts on A, the root of the key. Then it moves up to C-sharp, the third note in the A major scale. After A itself, C-sharp is the note that most defines the feeling of being in A major. The interval between A and C-sharp is a major third, and we in Western cultures have come to associate it with happiness.
In the second half of the first bar, the riff moves up to D, the fourth note of the A major scale. When you lift up from the major third to the fourth, it’s called a suspension, because that’s exactly what it feels like. When you’re released back down to C-sharp, the suspension is resolved.
If you start the A major scale on the fourth degree, D, and then keep moving around the scale, jumping to each alternating scale tone, you get the notes D, F-sharp, and A. These notes form a D major chord. Because it starts on the fourth note of A major, D major is known as the IV chord in A. When you play the notes in a chord one at a time, it’s called an arpeggio. The second bar of the “Stir It Up” riff starts with an arpeggio of the IV chord.
If you start the A major scale on fifth degree, E, and hop onto alternating scale tones, you get E, G-sharp, and B. These notes form the V chord in A. The second half of the second bar is an arpeggiated V chord.
Taken together, the whole chord progression is a bar of A, the I chord, followed by half a bar of D, the IV chord, and half a bar of E, the V chord. When a musician talks about a I-IV-V progression in A, this is what they’re talking about.
“Stir It Up” is at a Mother Goose level of harmonic simplicity. So why doesn’t it sound like a nursery rhyme? The answer lies in the groove. Before each half bar, there’s a little sixteenth note length pickup. It’s a small touch, but it’s enough to convey that reggae swing, and it locks the guitar part into the groove that’s bubbling along in the bass, drums, and keyboards. The guitar riff isn’t spelling out the chords in order to take you through a linear harmonic narrative. It’s using the chords to help orient you within the looped groove. Plenty of boring tunes use I-IV-V. It’s Bob Marley’s grooves that make his music distinctive.