You’ve probably hit it by accident. That sour, jarring note that makes your skin crawl and sounds like a mistake. It’s the flatted fifth. In music theory circles, we call it the tritone, and for centuries, it was literally nicknamed the "Devil in Music." But here’s the thing about the b5 chord on guitar: without that tension, rock, blues, and jazz would be incredibly boring.
Think about the opening riff of "Black Sabbath" by Black Sabbath. Tony Iommi leans hard into that G to C# interval. That C# is the flat five. It’s dark. It’s heavy. It’s basically the reason heavy metal exists as we know it today. But you don't have to be a doom metal enthusiast to use it. Honestly, it’s one of the most versatile tools in your bag if you want to add a little sophisticated "stink" to your playing.
Most guitarists stick to the basics. Major, minor, maybe a 7th chord if they're feeling fancy. But understanding how a b5 works changes how you see the fretboard. It’s not just a "wrong" note; it's a specific flavor of tension that demands a resolution.
What is a b5 chord on guitar anyway?
Let's strip away the jargon for a second. A standard power chord (a 5 chord) is built with a root and a perfect fifth. If you’re playing a G power chord, you’re playing G and D. To make it a G(b5), you just slide that D note down one fret to C#. That’s it. One fret. But that tiny move creates a massive shift in mood.
Mathematically, the interval is exactly half an octave. It splits the twelve notes of the Western scale right down the middle. This creates a physical phenomenon called "dissonance." Our ears naturally want to hear that flat five move up to the perfect fifth or down to the fourth. It’s unstable. It’s restless. It’s like a spring being pushed down, waiting to pop back up.
You'll see this chord written a few different ways in lead sheets. Sometimes it’s G(b5). Sometimes it’s G-5. In jazz, it’s often part of a m7b5 chord, which people call the "half-diminished" chord. Whatever you call it, the core DNA is that squeezed, tense interval between the root and that lowered fifth.
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Putting the b5 chord on guitar into practice
You can't just throw a b5 chord anywhere. If you try to end a happy folk song on a C(b5), your audience is going to look at you like you just insulted their mother. It's a bridge, not a destination.
The Blues Application
The "blue note" is actually the b5 of the minor pentatonic scale. When you’re playing a blues in E, that Bb note is your b5. You don't always play it as a full chord, but when you do, it adds a "mean" quality. Try playing an A7 chord and then sliding into an A7(b5). It sounds sophisticated and slightly dangerous. It’s the sound of the Delta.
The Jazz Connection
Jazz players live for the b5. They rarely play a straight 5th anyway. If you look at a classic II-V-I progression in a minor key—let’s say in D minor—the first chord is often an Em7b5. This chord (E, G, Bb, D) creates a pull toward the A7 that follows it. Without that Bb, the progression loses its emotional weight. It would just sound... polite. And jazz isn't supposed to be polite.
Heavy Metal and Hard Rock
I already mentioned Iommi, but look at Slayer or Metallica. The b5 chord on guitar is the foundation of the "locrian" sound they use to create dread. When you play a chromatic run that hits that b5, you’re tapping into a sound that feels unstable and aggressive. It’s a shortcut to making a riff sound "evil" without having to play at 200 beats per minute.
How to actually finger these chords
Don't overcomplicate it. If you know your movable barre chord shapes, you're halfway there.
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The Power Chord Version: Take your standard two-note power chord on the E and A strings. Move your pinky (or ring finger) back one fret. If you're at the 3rd fret (G), your index is on the 3rd fret of the E string and your other finger is on the 4th fret of the A string. Wait, no—that's a sharp 4. Let's try that again. Your index is on the 3rd fret of the E string, and your other finger is on the 4th fret of the A string if you're thinking of it as a #4, but for a b5, you're looking at the D string. Actually, the easiest way is to play the root on the A string, 3rd fret, and the b5 on the D string, 4th fret.
The "Hendrix" Style b5: If you're playing a 7#9 (the famous Hendrix chord), you can easily tweak it. But for a pure 7b5, try this: Middle finger on the G (3rd fret, E string), Ring finger on the F (3rd fret, D string), Pinky on the B (4th fret, G string). This leaves out the perfect fifth entirely and gives you a crunchy, biting sound that works wonders in a funk or blues context.
Why the "Tritone" used to be banned
There’s a common myth that the Catholic Church officially banned the tritone (the b5 interval) in the Middle Ages because it was "Diabolus in Musica." While there isn't a specific papal decree that says "thou shalt not play a b5," it was definitely frowned upon.
Music back then was about reflecting the perfection of God. Perfect fifths and octaves were seen as "pure" because their mathematical ratios are simple ($2:3$ and $1:2$). The b5? Its ratio is much more complex ($\sqrt{2}:1$). It sounded chaotic. It didn't resolve. In a world that valued order, the b5 was the ultimate symbol of disorder.
Fast forward to the 20th century, and that disorder became the voice of the marginalized. Blues musicians used it to express the pain of the Jim Crow South. Be-bop players like Charlie Parker and Dizzy Gillespie used it to break away from the "sweet" sounds of big band swing. They took the "devil" and made it art.
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Common misconceptions about the b5
I hear this a lot: "A b5 chord is just a diminished chord." Not exactly. A diminished triad is built with a root, a minor third, and a diminished fifth (the b5). A b5 chord, in its purest form, might keep the major third.
If you play a C Major chord (C, E, G) and change it to C(b5) (C, E, Gb), you have a very different vibe than a C diminished triad (C, Eb, Gb). The major third against the flat five is incredibly clashing—it’s what we call a "Lydian Dominant" sound. It’s dreamier, almost like something out of a film noir soundtrack.
Another myth is that you can't use it in pop music. Total nonsense. Check out "The Simpsons" theme song. The very first interval—"The Simp-sons"—is a C to an F#. That’s a b5. It’s quirky, memorable, and cuts through the mix like a knife.
Actionable steps for your practice session
If you want to master the b5 chord on guitar, don't just memorize the shapes. You have to train your ears to hear where they want to go.
- The Resolution Drill: Play a G7(b5) chord. Listen to the tension. Now, move all your fingers to a CMaj7 or a C6. Feel that "ahhh" moment? That’s resolution. Practice moving from the tense b5 to a stable chord a fourth away.
- The Scale Integration: Next time you’re soloing in the A minor pentatonic, find the Eb (6th fret on the A string or 8th fret on the G string). Don't just pass through it. Hang on it. Shake it with some vibrato. Then slide down to the D or up to the E. Hear how it adds that "greasy" blues feel.
- The Songwriter Challenge: Write a four-bar progression. Use standard chords for the first three bars (like Am - Dm - G7), but for the fourth bar, use a Db7(b5) before going back to Am. It’s a "tritone substitution," a classic jazz move that works because the Db(b5) shares the same dissonant notes as a G7.
The b5 chord on guitar is essentially a tension delivery system. It’s the cliffhanger at the end of a TV episode. It’s the spicy pepper in a bland meal. You don't want a whole plate of peppers, but without them, you’re missing the point of the dish.
Start small. Find one shape you like. Use it once in a song. Notice how it makes you feel. Usually, that feeling is a mix of unease and excitement. That’s the power of the flat five. It forces the listener to pay attention because they’re waiting for the other shoe to drop. Once you get comfortable with that "ugly" sound, you’ll realize it’s actually one of the most beautiful tools you have for telling a story with your music.
To really get this under your fingers, grab your guitar right now and find a standard 7th chord shape. Identify where the 5th is. Lower it by one fret. Play it. Then, immediately play the chord a half-step down or a fourth up. Your ears will tell you exactly why this chord has survived centuries of being called "evil." It just sounds too good to ignore.