An interval is the distance between two notes measured in semitones. The chromatic scale has 12 semitones in an octave, giving us 12 distinct intervals. Every chord, scale, and melody in Western music is built from combinations of these 12 distances.
- THE TWELVE INTERVALS (from smallest to largest):
- MINOR 2nd (1 semitone): C to C#. The smallest step. Used in chromatic passages. Creates tension and dissonance. The 'Jaws' theme is built on repeated minor 2nds.
- MAJOR 2nd (2 semitones): C to D. The standard step in major and minor scales. Neutral, connecting.
- MINOR 3rd (3 semitones): C to Eb. The interval that defines minor chords. Darker, more introspective. The gap from the root to the third of any minor chord.
- MAJOR 3rd (4 semitones): C to E. The interval that defines major chords. Brighter, more open. The gap from the root to the third of any major chord.
- PERFECT 4th (5 semitones): C to F. Stable and open. Found in quartal harmony (jazz, folk). 'Here Comes the Bride' begins with a perfect 4th.
- TRITONE (6 semitones): C to F#/Gb. Exactly halfway through the octave. Maximum dissonance in the Western ear - historically called diabolus in musica (the devil in music). The V7 chord's internal tension is created by the tritone between its 3rd and 7th. 'The Simpsons' theme opens with a tritone.
- PERFECT 5th (7 semitones): C to G. The most stable interval after the octave. Power chords in rock are root + perfect 5th. Hollow, open, powerful.
- MINOR 6th (8 semitones): C to Ab. Melancholic quality. Used extensively in ballads and blues.
- MAJOR 6th (9 semitones): C to A. Warm and open. The interval between the root and sixth of a major chord. 'My Bonnie Lies Over the Ocean' begins with a major 6th.
- MINOR 7th (10 semitones): C to Bb. Used in dominant 7th chords and blues scales. Slightly unresolved, forward-leaning.
- MAJOR 7th (11 semitones): C to B. The leading tone - one semitone below the octave, creating strong upward pull. Used in major 7th chords for a jazzy, sophisticated quality.
- OCTAVE (12 semitones): C to C. The same note, doubled in frequency. Perfect consonance.
CONSONANCE VS. DISSONANCE: Intervals are rated by their relative stability. Perfect consonances (octave, 5th, 4th) are the most stable. Imperfect consonances (major/minor 3rds and 6ths) are stable but have color. Dissonances (major/minor 2nds, major/minor 7ths, tritone) are unstable and create forward motion.
EAR TRAINING SHORTCUT: Associate each interval with a familiar melody. Minor 2nd = Jaws. Major 2nd = Happy Birthday (first two notes). Minor 3rd = Smoke on the Water. Major 3rd = When the Saints Go Marching In. Perfect 4th = Here Comes the Bride. Tritone = The Simpsons. Perfect 5th = Star Wars theme. Major 6th = My Bonnie. Minor 7th = Somewhere (West Side Story). Major 7th = Take On Me (the ascending synth line). Once you hear these anchors, you can identify any interval in music.
The theoretical significance of intervals extends far beyond simple distance measurement. Intervals carry aesthetic and emotional qualities that have been codified by music theorists across centuries. The perfect fourth and fifth were the consonances prized in medieval organum, the earliest form of polyphony, precisely because their simple frequency ratios (3:2 for the fifth, 4:3 for the fourth) produce stable, open-sounding harmony. Renaissance counterpoint classified intervals into a hierarchy: perfect consonances (unison, fifth, octave), imperfect consonances (thirds and sixths), and dissonances (seconds, sevenths, and tritones), with strict rules governing how dissonances could be approached and resolved. This classification system reflected both acoustic mathematics and cultural values about musical beauty that shaped Western composition for centuries.
The tritone — the interval spanning exactly half an octave, six semitones — holds a unique position in this history. Medieval theorists called it diabolus in musica (the devil in music) because its instability and tendency to resolve made it seem dangerous in sacred contexts. Yet this same instability became the engine of functional tonal harmony: the dominant seventh chord's characteristic tension comes from the tritone formed between its third and seventh scale degrees, and the resolution of this tritone — inward by semitone in contrary motion — creates the sense of arrival that defines the V7-I cadence at the heart of Western harmonic practice. Franz Liszt exploited the tritone's symmetrical properties to create ambiguous harmonies that could resolve to multiple tonal centers, anticipating the harmonic language of late Romanticism. In jazz, tritone substitution — replacing a dominant seventh chord with the dominant seventh chord a tritone away — became a standard improvisational device after bebop, exploiting the fact that the two chords share the same tritone interval (though with the third and seventh exchanged). Understanding intervals as both acoustic phenomena and culturally loaded units of musical meaning reveals the deep continuity between music theory and musical expression across radically different historical contexts. The student who develops interval recognition not merely as an abstract skill but as a form of perceptual attunement — learning to hear intervals as expressions of specific tension, stability, brightness, or darkness — gains an analytical tool that transforms how they perceive and engage with every piece of music they encounter, making interval study one of the highest-yield investments in any musician's theoretical education. The ability to identify, sing, and play any interval on demand is a foundational skill that supports every other area of musical study, from sight-reading and ear training to harmonic analysis and composition, making it one of the most important early investments in any comprehensive musical education.