Perfect Fourth Interval

perfect fourth overview

A perfect fourth spans five half steps. From C, for example, a perfect fourth up is F. The number in its name counts the letter names it covers, including both ends: from C to F, C D E F is four, so it is a fourth. The five half steps make it perfect. Fourths and fifths, like unisons and octaves, are called perfect: they have no major or minor form.

Lesson Steps

Add a header to begin generating the table of contents

The perfect fourth sounds open and a little hollow. Played together it is less settled than a fifth, and in the bass it often wants to move. As a leap in a melody it’s very common: many melodies begin by rising a fourth from the 5th of the key to the tonic, from G up to C in C major.

On the keyboard, a perfect fourth always has four keys between its two notes. Depending on where it starts, those notes can fall on white or black keys, which gives it four different shapes.

The shapes of the perfect fourth 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 white key: C to F

Perfect fourths that share this same shape are C–F, D–G, E–A, G–C, A–D, and B–E. There are four keys in between (two white, two black).

White key to black key: F to B♭

F–B♭ is the only perfect fourth with this shape. There are four keys in between (two white, two black).

Black key to white key: F♯ to B

F♯–B is the only perfect fourth with this shape. There are four keys in between (two white, two black).

Black key to black key: D♭ to G♭

Perfect fourths that share this same shape are D♭–G♭, E♭–A♭, A♭–D♭, and B♭–E♭. There are four keys in between (three white, one black).

Reading the perfect fourth on the staff

A fourth goes from a line to a space, or from a space to a line, with one line and one space in between. That stays true whatever the accidentals are: every fourth looks like a fourth, and the accidentals tell us its quality.

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 fourth recognizes it everywhere.

The perfect fourth in the hand

Fourths often fall under 1 and 4 or 2 and 5. In a five-finger pattern, a fourth is the distance from the thumb to the 4th finger, with two fingers skipped in between.

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 perfect fourth

If we move the lower note up an octave (or the upper note down one), a perfect fourth becomes a perfect fifth: C to F turns into F to C. The numbers of an interval and its inversion add up to nine, and their half steps to twelve (5 + 7). A perfect interval stays perfect.

On the keyboard the shapes swap as well: a white-to-black shape inverts to a black-to-white one, and a white-to-white shape stays white to white.

Practice the perfect fourth

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 perfect fourth.
Play a perfect fourth up from all twelve keys, naming the upper note as we go.
Read it: look for perfect fourths 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 perfect fourth

Assuming every white-key fourth is perfect. Six of the seven are, but F up to B is a tritone. The perfect fourth from F needs B♭.
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.