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Tritone (Augmented 4th / Diminished 5th)

tritone overview

A tritone spans six half steps. From C, for example, a tritone up is F♯. Its name counts whole steps: C to D, D to E, E to F♯ is three of them.

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It is also the one interval with two common names on the staff. Written as a fourth (C to F♯, four letter names), it is an augmented fourth; written as a fifth (C to G♭, five letter names), it is a diminished fifth. On the keyboard the two are the same keys.

The tritone divides the octave exactly in half. It’s the most restless interval of the thirteen. Inside a dominant 7th chord, the 3rd and the 7th form a tritone (B and F in G7), and the way those two notes resolve, B up to C and F down to E, is much of what makes the chord lead home. It is also the outer interval of a diminished chord.

Five keys always lie between its two notes. Depending on where we start, the notes fall on white or black keys in three different ways, and since each can be spelled both ways, we look at six shapes below.

The shapes of the tritone on the piano

Each shape sits a little differently under the hand, so it is worth knowing them all. Under each keyboard, the same notes are on the staff: played together, then up, then down.

White key to black key, as an augmented 4th: C to F♯

Augmented fourths that share this same shape are C–F♯, D–G♯, E–A♯, G–C♯, and A–D♯. There are five keys in between (three white, two black).

White key to black key, as a diminished 5th: C to G♭

Diminished fifths that share this same shape are C–G♭, D–A♭, E–B♭, G–D♭, and A–E♭. There are five keys in between (three white, two black).

White key to white key, as an augmented 4th: F to B

F–B is the only augmented fourth with this shape. There are five keys in between (two white, three black).

White key to white key, as a diminished 5th: B to F

B–F is the only diminished fifth with this shape. There are five keys in between (three white, two black).

Black key to white key, as an augmented 4th: D♭ to G

Augmented fourths that share this same shape are D♭–G, E♭–A, G♭–C, A♭–D, and B♭–E. There are five keys in between (three white, two black).

Black key to white key, as a diminished 5th: C♯ to G

Diminished fifths that share this same shape are C♯–G, D♯–A, F♯–C, G♯–D, and A♯–E. There are five keys in between (three white, two black).

Reading the tritone on the staff

On the staff, the tritone has two looks. As an augmented fourth (C to F♯) it goes from a line to a space, or a space to a line, like any fourth. As a diminished fifth (C to G♭) it goes from a line to a line, or a space to a space, with one line or space in between, like any fifth. The staff shows the number; the accidental tells us it is a tritone rather than a perfect fourth or fifth.

This is what makes intervals so useful for reading. Rather than naming every note from the clef, we read from one note to the next: once we know where we are, the shape on the staff tells us how far to move. Reading this way is relational rather than absolute, and it is much faster.

It works the same in the treble and bass clef, and at any height on the staff, so a reader who knows the look of a tritone recognizes it everywhere.

The tritone in the hand

The tritone sits between a fourth and a fifth, so it often falls under 1 and 4, 2 and 5, or 1 and 5, depending on the notes around it. Here the shape matters more than usual: with one note on a black key, the hand turns slightly to reach it.

The spacing on the staff and the spacing in the hand belong together. In a five-finger pattern, a step on the staff is often the next finger, and a skipped note a skipped finger, so the distance we see becomes a distance we feel.

Inverting the tritone

Turned upside down, a tritone is still a tritone: six half steps up from C is F♯, and six half steps up from F♯ is C again. The spelling flips, though: an augmented fourth inverts to a diminished fifth, and a diminished fifth to an augmented fourth.

Practice the tritone

Play the first shape, C to F♯, together and then one note after the other, and listen to the sound before moving on.
Find the same shape at every place it occurs on the keyboard (the lists under each image), then the other shapes. Notice how the hand changes as the keys change color, while the sound stays a tritone.
Play a tritone up from all twelve keys, naming the upper note as we go.
Read it: look for tritones in a piece we know, and before playing each one, name the interval from its look on the staff.
Once the shapes are reliable, play the interval without looking at the hands, feeling the span between the fingers.

Avoid common mistakes with the tritone

Mixing up the two spellings. C to F♯ and C to G♭ are the same keys, but one is a fourth on the staff (augmented) and the other a fifth (diminished). Which one we see depends on the key and on where the notes are going.
Counting keys instead of half steps. The starting key isn’t counted: from C, the first half step is C♯.
Reading every note from the clef. Naming each note separately is slow. Reading the interval from the previous note is what lets the eye stay ahead of the hands.