What is the perfect fourth interval?
The perfect fourth spans five semitones, sitting precisely between the major third and the perfect fifth in the harmonic series. Written upward from C it reaches F, creating one of music's most recognizable and versatile intervals. While the perfect fourth shares the same acoustical purity as the perfect fifth, its role in harmony shifts depending on context—appearing consonant in medieval organum yet treated as a dissonance requiring resolution in classical voice leading.
Unlike the tense tritone that demands immediate resolution, the perfect fourth occupies a middle ground, creating an open, suspended quality that pulls gently toward the third. This ambiguous character makes it indispensable in suspension figures, quartal voicings, and contemporary chord extensions. From Gregorian chant to modern jazz, the perfect fourth has shaped harmonic language across centuries and styles.
Theory and harmonic context
In traditional tonal harmony, the perfect fourth functions as a consonance when supported by a lower voice but becomes a dissonant suspension when placed above the bass without proper preparation. This dual nature stems from the overtone series, where the fourth appears relatively early but inverts to create a perfect fifth when flipped. Classical composers exploit this tension through the ubiquitous 4-3 suspension, where the fourth hangs momentarily before resolving down a step to the third, releasing accumulated harmonic pressure.
Modern harmony embraces the perfect fourth in stacked quartal chords, where composers build sonorities entirely from fourths rather than traditional thirds. This technique, prevalent in jazz and film scoring, produces an ambiguous, floating quality that avoids strong tonal centers. The fourth also defines suspended chords— sus4 and 7sus4 voicings replace the third with a fourth, creating harmonic tension that typically resolves inward to a stable triad or seventh chord.
- Semitone distance: five steps (0 → 5)
- Scale-degree relationship: root to fourth in major and minor keys
- Enharmonic stability: always spelled as a perfect fourth (not augmented third)
- Typical resolution: downward by step to the third
Suspended chords and voice leading
Suspended fourth chords form the cornerstone of contemporary pop, rock, and worship music, replacing the defining third of a major or minor triad with a fourth that hovers in harmonic limbo. A Csus4 chord (C-F-G) lacks the character-defining third, creating an open, unresolved sound that begs for forward motion. When the fourth (F) resolves down to the third (E), the suspended tension melts into the bright consonance of C major, completing one of music's most satisfying gestures.
Voice leading principles dictate that suspensions prepare, sustain, and resolve—the fourth enters as a consonance in the previous chord, persists through a change of harmony where it becomes dissonant, then steps down to resolve the tension. Baroque composers perfected this technique in figured bass, notating 4-3 suspensions to indicate the expected voice motion. Modern arrangers extend the concept by stacking multiple fourths in parallel motion, creating dense quartal harmonies that sidestep traditional tertian chord construction entirely.
Recognizing the perfect fourth
The perfect fourth delivers an instantly recognizable sound—open, stable, and slightly yearning. Train your ear with iconic melodic references: the opening two notes of "Here Comes the Bride" (Wagner'sBridal Chorus), the fanfare beginning of "Amazing Grace," or the first interval in Auld Lang Syne. Each example leaps upward by a perfect fourth, creating a sense of lift without the bright triumph of a fifth or the gentle warmth of a third.
When practicing interval recognition, sing the perfect fourth against a sustained tonic, then resolve it down by step to hear how naturally it wants to settle into the third. Compare it directly with a tritone—just one semitone wider but dramatically more tense—to internalize the difference between suspension and instability. Alternate between fourths and fifths to feel how the fourth reaches upward while the fifth grounds downward, establishing complementary roles in harmonic motion.
Practice and application
Begin by mapping every perfect fourth across the keyboard, pairing each white key with its partner five semitones above. Play these intervals blocked (simultaneously) and broken (sequentially), internalizing the physical distance and aural quality in both directions. Next, embed the fourth into common suspended chord progressions—cycle through Csus4 to C, Fsus4 to F, and Gsus4 to G, focusing on the resolution moment where tension releases into consonance.
Extend your study by improvising melodies that emphasize the fourth as a leaping interval, then resolve those leaps downward by step. Explore quartal voicings by stacking three or four perfect fourths vertically—C-F-B♭-E♭ creates a modern, ambiguous sonority common in jazz and film music. Finally, compose short phrases using 4-3 suspensions over a simple bass line, alternating between preparation, suspension, and resolution to master the interval's voice-leading power across multiple harmonic contexts.