Once you know where the notes are in your pentatonic scale, the next step is connecting them to the chords you’re playing over. That’s where I-IV-V comes in.
This is the third lesson in my blues scale series, and it builds directly on what you learned about finding your tonic. If you haven’t watched that one yet, go back and check out understanding the tonic in your scale first. You’ll need it for this to make sense.
What Is I-IV-V Anyway?
In blues and rock, almost every progression uses some combination of the I, IV, and V chords. These are the first, fourth, and fifth chords in a key. In the key of A, that’s A (the I), D (the IV), and E (the V).
Here’s what’s cool: those same letter names – A, D, and E – are also notes in your scale. When you’re soloing, hitting those specific notes while those chords are playing creates a strong, grounded sound. You land on safe notes that harmonize perfectly with what’s happening underneath you.
Now, there’s a bit of music theory weirdness here. The pentatonic scale only has five notes. If you count from the tonic (1-2-3-4-5), you get all five notes. But when I talk about “the 4 and the 5,” I’m talking about the fourth and fifth letter names out of the complete diatonic scale – not the fourth and fifth notes in the pentatonic. It’s confusing, I know. But stay with me.
The easier way to think about it: you’re just finding three letter names. In A minor, you’re finding A, D, and E on your fretboard. That’s it.
The Perfect Harmony Box
I call the I-IV-V pattern the “perfect harmony box.” It’s a shape that repeats all over your guitar neck, and once you see it, you can’t unsee it.
Here’s how it works in the A minor pentatonic scale:
Start with your tonic – your “one.” Let’s say you’re on the 5th fret of the 6th string. That’s your A.
Cross directly to the next string, same fret. That’s your “four” – the D note.
From that D, move up two frets. That’s your “five” – the E note.
Cross directly across from that E to the next string, same fret. You’re back to your tonic – another A, one octave higher.
So you’ve got A (1), D (4), E (5), and A (octave) – all in a box shape. That pattern works anywhere on the lower strings.
The B String Problem
This pattern works great on the 6th, 5th, 4th, and 3rd strings because those strings are all tuned in perfect fourths. E to A is a fourth. A to D is a fourth. D to G is a fourth.
But then you hit the G to B string, and things get weird. The B string is tuned a major third higher than the G string – one fret less than a fourth. That’s why when you tune your guitar by ear, you use the 5th fret for most strings, but you have to use the 4th fret to tune the B string.
What does that mean for finding your I-IV-V? When you cross from the G string to the B string, you need to add one fret to compensate.
Let’s say you’re finding your I-IV-V on the higher strings. You’ve got your tonic (the 1) on the 3rd string, your 4 on the 2nd string, and your 5 two frets up from that. When you cross from the 2nd string to find your octave on the 1st string, you’d normally go straight across. But because of that B string tuning, you have to move up one fret instead.
It’s annoying, but once you know it, you just automatically make that adjustment.
Finding I-IV-V Anywhere
The beauty of this system is you can use it anywhere. Pick any note on the lower four strings, and you can immediately find its I-IV-V.
Let’s try it in E. Say your tonic is the 12th fret on the 6th string (that’s an E). Cross directly to the 5th string, 12th fret – that’s your A (the IV). Move up two frets to the 14th fret – that’s your B (the V). Cross over to the 4th string, 14th fret, and you’re back to E (the octave).
You can do this starting from any position in your pentatonic scale. The pattern stays the same. It’s just I-IV-V-octave, over and over.
Why This Matters for Your Solos
When you know where these notes are, you start to have real options. Instead of just running up and down the scale hoping something sounds good, you can target specific notes at specific moments.
Playing over an A chord? Land on an A note.
Chord changes to D? You know exactly where to find a D.
Back to the A? You’ve got multiple A notes to choose from all over the neck.
These three notes – the 1, 4, and 5 – are your foundation. They’re the most important harmonic points in any blues progression. Hit them at the right time, and your solos sound intentional. Miss them, and you’re just wandering.
The Pattern Repeats Everywhere
Once you get comfortable with this box shape, you’ll start seeing it everywhere. It shows up in every position of the scale. You can start from different tonic notes and build the same box around them.
That’s the whole point of learning your scales this way. It’s not about memorizing shapes. It’s about understanding the relationships between the notes so you can navigate the fretboard like you actually know what you’re doing.
And look, you don’t need to be a technical genius to get this. You just need to understand the pattern. I-IV-V. The perfect harmony box. It’s the same everywhere you go on the guitar.
Practice This Today
Grab your guitar and find your tonic in the A minor pentatonic scale. Then find the 4 and the 5. Play them. Listen to how they sound. Now move to a different tonic and do it again.
Do that in a few different spots on the neck. Get used to the shape. Once it’s in your fingers, you’ll have a framework you can use in every solo you play.
This is how you stop getting lost. This is how you start playing with intention. Learn the I-IV-V, and you’ll know exactly where you are and where you’re going.
Once you’ve got the I-IV-V locked in, the next step is adding chromatic passing notes to connect your scale tones. Those half-step approaches are what make your lines sound smooth and intentional instead of just jumping from note to note.
For a complete breakdown of the blues scale and how all these concepts fit together, check out my full guide to the blues scale. It covers the whole progression from basic pentatonic to full blues mastery.
Now get to work on it. In my 45 years of playing, I’ve never met a solid blues guitarist who didn’t know their I-IV-V cold.