What Is a Tritone Interval? The ‘Forbidden Chord,’ Finally Explained

No interval in music has a criminal record like the tritone. It’s been called the devil’s interval and the forbidden chord; legend says the medieval church banned it; the internet insists a certain famous rock intro is ‘banned’ in guitar stores because of it. Behind all the folklore sits something much simpler and far more useful: a specific, learnable sound — six half-steps of pure tension — that powers the blues, drives film scores, and hides inside chords you probably already play.

This lesson covers the whole story: what a tritone actually is, how to find and play it on your guitar (diagrams included), why it sounds so unstable, the honest truth behind the legends — and the resolution trick that turns music’s most notorious tension into its most satisfying release.

What a Tritone Actually Is

A tritone is the distance of exactly six half-steps between two notes — for example, C up to F♯. The name means ‘three whole tones’ (three whole steps of two half-steps each), and depending on how it’s spelled in written music, you’ll see it called an augmented 4th or a diminished 5th — two names, one identical sound. Six half-steps has one remarkable property: it’s exactly half of the twelve-step octave. The tritone sits at the precise midpoint between a note and its octave — as far from ‘home’ as a note can get — and that geometry, as we’ll see, is the whole secret of its sound.

Find It on Your Guitar in Ten Seconds

The fastest way to understand any interval is to play it, and the tritone couldn’t be easier to find. Method one — one string: pick any note, then play the note six frets higher on the same string. That leap is a tritone, anywhere on the neck, every time. Play the two notes one after another, and you’ll recognize the sound instantly: sirens, suspense scenes, the opening of a thousand heavy riffs.

Method two — the movable two-note grip, for hearing both notes together: on any of the lower string pairs tuned a fourth apart (strings 6–5, 5–4, or 4–3), fret a note, then fret the adjacent higher string one fret higher. That two-finger shape is a tritone, and it slides anywhere on the neck. Strum just those two strings and enjoy the delicious wrongness.

Why It Sounds So Unstable

Here’s the honest, jargon-free version. Our ears constantly track how far notes are from resolving back toward stability — and the tritone, sitting at the octave’s exact midpoint, is maximally ambiguous: it leans equally in both directions and settles in neither. It is, quite literally, the sound of being halfway — and halfway is the one place music can’t rest. That’s not a flaw; it’s a feature. Music runs on tension and release, and the tritone is the most concentrated dose of tension the twelve notes can produce. Which is exactly why composers never actually threw it away — they saved it for the moments that needed it most.

The Legends, Honestly Fact-Checked

• ‘The church banned it’ — mostly legend. Medieval theorists really did nickname the tritone diabolus in musica — ‘the devil in music’ — and singers were taught to avoid it in sacred melodies because it was considered awkward and unstable to sing. But there’s no record of an official ban or punishment; the ‘forbidden’ reputation is a colorful exaggeration of what was essentially old-school voice-leading advice. The nickname, however, is entirely real — and honestly, it earned it.
• ‘That famous rock intro is banned’ — a joke that escaped. The ‘banned in guitar stores’ idea comes from a famous comedy-film gag about overplayed songs, not from the tritone or any real prohibition. The two legends fused online into ‘the forbidden riff,’ and search engines have been confused ever since. Nothing is banned; everything is folklore — but the folklore is genuinely fun, which is why it survives.
• What’s NOT legend: the tritone’s starring role in real music. It’s the engine inside every dominant 7th chord (the sound of blues and jazz wanting to resolve), the core of the diminished chords we’ve covered elsewhere, the backbone of countless metal riffs, and Hollywood’s favorite shortcut to unease. The devil’s interval turned out to be one of music’s hardest workers.

The tritone in one line: Six half-steps — the exact midpoint of the octave — spelled as an augmented 4th or diminished 5th, nicknamed the devil’s interval, never actually banned, and quietly powering blues, jazz, metal, and film music ever since.

The Payoff: Tension That Resolves

The tritone’s best trick is what happens when it lets go. Because both of its notes lean toward stability, each can move just one fret — in opposite directions — and land on the most restful sound in music. Play this with two fingers: B and F together (a tritone), then move B up one fret to C and F down one fret to E. Tension, then home. That two-fret move is the beating heart of the dominant-7th-to-home resolution that ends a thousand songs — and once you’ve played it slowly, you’ll start hearing it everywhere.

The Takeaway

The ‘forbidden chord’ is a tritone: six half-steps, the octave’s midpoint, music’s purest concentrated tension — nicknamed the devil’s interval by medieval theorists, never actually banned by anyone, and indispensable to the music you love precisely because of how badly it wants to resolve. You can find it in ten seconds on one string, hold it in a two-finger movable grip, and release its tension with the oldest two-fret move in harmony. The legends are fun; the sound is better. And if this is the kind of theory that makes your playing make sense, it’s a sign of what learning at the right level feels like.

Further Reading

• The Tritone on Guitar, Explained — shapes, chords, and how to actually use this sound
• Diminished vs Augmented Chords — the chords built from stacked tritone tension
• What Is the 1-3-5 Chord Rule? — the foundation all of this counting stands on
• What Comes After Learning the Basics? — where theory fits your roadmap