The flatted fifth. The devil’s chord. The devil’s interval.

If you lived long enough ago, they’d have hung you for playing it.

Back in the Middle Ages, the Catholic Church banned a specific musical interval and called it Diabolus in Musica — the Devil in Music. Composers who used it could be punished. Some were executed. All for playing one note that sat in the “wrong” place.

Fast forward a few hundred years, and that same forbidden note became the backbone of the blues. And rock. And jazz. And metal.

In this lesson, we’ll walk through exactly what the flatted fifth is, where to find it on your fretboard, and why it sounds the way it does. We’ll also play some instantly recognizable riffs that use it — and you’ll probably realize you’ve been playing this note for years without knowing what it was called.

Where the Flatted Fifth Lives in the Scale

If you’ve been working with the minor pentatonic scale, you already know five notes. In the key of A minor, that’s A, C, D, E, and G. Five notes, two notes per string in the standard box position.

The flatted fifth sits in the gap between the 4th degree (D) and the 5th degree (E). It’s the note right in between — Eb (or D#), one fret above your 4th and one fret below your 5th.

It’s a chromatic passing note — one of those “in-between” notes that doesn’t belong to the pentatonic scale but adds a specific flavor when you use it. And the flavor the flatted fifth adds? Dark. Tense. Unresolved. Bluesy.

That’s why it earned the nickname “the blues note.” When you add this one chromatic tone to your minor pentatonic, you get the full blues scale — six notes instead of five.

What the Flatted Fifth Sounds Like

The flatted fifth creates what musicians call dissonance — a sound that doesn’t resolve neatly. It pulls in two directions at once. Your ear wants it to go somewhere, and that tension is exactly what makes it powerful.

Play the interval on its own and you can hear that dark, unsettled quality immediately. One note to the flatted fifth — it just hangs there. It’s not comfortable. And that discomfort is the whole point.

That’s why the medieval Church was so spooked by it. In an era where music was supposed to reflect divine order, a note that sounded this restless was considered dangerous.

But blues players figured out that tension is the engine of emotion. Lean into the flatted fifth, and your solo suddenly has grit, edge, and feeling that the straight pentatonic can’t deliver on its own.

How to Find It in Any Key

Technically, the flatted fifth is the perfect fifth interval lowered by one semitone — one fret. So in any key, you find your root, count up to the 5th, and drop it down one fret.

In practice, most guitar players find it relative to their pentatonic box. Here’s how it works in A minor pentatonic, Position 1 (5th fret):

• 6th string: Your A is at fret 5, your C is at fret 8. The flatted fifth (Eb) lives up on the 6th fret of the 5th string — but you’ll feel it most between the 4th and 5th degrees.
• 5th string: D is at fret 5, E is at fret 7. The flatted fifth sits at fret 6 — right in the middle. This is probably the most common spot to play it.
• 4th string: G is at fret 5, A is at fret 7. The Eb is at fret 8 on this string, up in the next octave.

The beauty of the guitar is that these shapes are moveable. Shift the whole pattern to a different fret and you’re in a different key, but the flatted fifth is always in the same relative position — one fret above the 4th degree.

Using It as a Passing Tone vs. a Landing Note

Here’s the thing — the flatted fifth “can be used in a lot of different ways.” It’s not a one-trick note.

That said, most of the time you’ll use it as a passing tone — a note you move through rather than a note you camp on. Slide through it on the way from the 4th to the 5th. Bend up into it. Let it create a flash of tension before resolving to a safer note.

But you can also land on it for effect. When you hold the flatted fifth, you get that dark, heavy sound that’s all over metal and hard rock. Think of the opening riff of Black Sabbath’s self-titled song — that’s a tritone (another name for the flatted fifth) played as a deliberate, sustained interval. It’s not passing through. It’s sitting there, making you uncomfortable on purpose.

The key is intention. When you know what the flatted fifth sounds like and where it lives, you can choose when to use it — and how long to stay on it — for maximum musical impact.

Where You’ve Already Heard It

Once you know what the flatted fifth sounds like, you start hearing it everywhere. In the lesson above, we play through several recognizable riffs — and you’ll probably realize you’ve been playing some of them already.

Jimi Hendrix used the flatted fifth constantly. That dark, psychedelic tension in “Purple Haze” and dozens of other songs? Flatted fifth. B.B. King leaned into it during his most emotional bends. Stevie Ray Vaughan built entire solos around the push and pull between the blues note and the rest of the pentatonic scale.

It shows up in jazz as dominant chord tensions. It shows up in metal as power chord riffs. It shows up in funk as chromatic bass lines. The flatted fifth isn’t a blues-only note — it’s a musical universal that the blues just happened to claim first.

Single Notes and Chords

The flatted fifth works in both single-note lines and chords. Most of this lesson focuses on single-note playing — runs, licks, and passing tones within the pentatonic framework.

But when you use it in a chord context, the effect is even more dramatic. A standard power chord with a flatted fifth instead of a perfect fifth creates a diminished sound — harsh, unstable, and full of tension. That’s the chord that terrified the medieval clergy.

If you want to hear the difference, play a standard A5 power chord (A and E). Then lower the E by one fret to Eb. Same root, but that one-fret change transforms the whole character of the chord from stable and strong to dark and restless.

The Flatted Fifth and the Blues Scale

The relationship between the flatted fifth and the blues scale is simple: the flatted fifth IS the note that turns the minor pentatonic into the blues scale.

Minor pentatonic: 1, b3, 4, 5, b7
Blues scale: 1, b3, 4, b5, 5, b7

One note. That’s all that separates the two scales. But what a difference that one note makes. The pentatonic sounds clean and safe. Add the flatted fifth, and suddenly the scale has an edge — a bluesy, gritty quality that changes everything about how your licks and solos feel.

If you’ve been working through the blues scale lessons in this series, the flatted fifth is the piece that ties it all together. You already know your I-IV-V chord tones and your chromatic passing notes. The flatted fifth is the most famous and most powerful of those passing tones — the one that defines the blues sound.

Try It Yourself

Have fun experimenting with this one. Tear it up.

Start simple. Play your A minor pentatonic box at the 5th fret. Find the flatted fifth on each string — it’s always one fret above the 4th degree. Play through the scale and add the blues note in. Slide through it. Bend into it. Hold it and let it ring.

Then put on a 12-bar blues backing track and experiment. Use the flatted fifth as a passing tone in your runs. Try landing on it at the end of a phrase and see how that tension feels. The more you use it, the more natural it becomes — and the more your solos start to sound like the blues players you admire.

The note that once got people killed is now the note that makes the blues sound like the blues. That’s a pretty good redemption story.