Perfect 4th

General info

Name

Perfect 4th

Quality

Perfect

Degree distance

4 degrees

Semitones

5

Short description

Five semitones. A sense of stability, often heard as a "transitional" interval.

Interval structure

Lower note

Root

Upper note

Perfect fourth (4)

Degree formula

II5 stIVIV

Semitone formula

5 semitones (2.5 tones)

Interval construction

Interval formula

P4

How it's built

From the root, move up by five semitones (two and a half tones, five frets on guitar).

Brief explanation

The perfect 4th is one of the "perfect" intervals. It sounds open and stable, but in a chord context can act as a suspension (sus4) that needs to resolve to the 3rd.

How the interval sounds

Sound character

The perfect 4th sounds open, "hollow," with a sense of transition or expectation. It is a "questioning" interval — a melodic leap of a 4th creates a sense of beginning a phrase. Standard guitar tuning (E-A-D-G) is based on 4ths. The sound is clean, bright, without emotional coloring.

Consonance / dissonance

Explanation

The perfect 4th holds a special place: melodically, it is a consonance; harmonically, it depends on context. If the 4th sounds above the bass (without a 3rd), it can be perceived as a suspension and be unstable. In parallel motion, 4ths are considered "hollow" (organum).

Tendencies & resolutions

Behavior

In a chord context, the 4th often acts as a suspension (sus4) and tends to resolve down to the 3rd (by a half step or whole step). Melodically, the 4th is stable and does not require mandatory resolution. The I → IV bass motion is a foundation of cadential movement.

Harmonic context

Context

The 4th does not appear in standard triads, but is the basis of sus4 chords and quartal harmony. In jazz, quartal harmony (chords built in 4ths) is a key technique. The 4th is present in all major and minor scales.

Interval inversion

Interval from every note