What is a Music Interval?
A music interval is the distance in pitch between two notes, measured by the number of scale steps or semitones that separate them. Intervals are one of the most fundamental concepts in music theory because they are the building blocks of scales, chords and melodies. Every chord you hear is made up of intervals stacked on top of each other, and every melody moves through a sequence of intervals. Being able to identify intervals quickly by sight is an essential skill for any musician learning to sight read.
How Intervals are Named
Intervals have two components to their name — a number and a quality. The number describes how many letter names the interval spans, counting both the starting and ending note. For example, C to E spans three letter names (C, D, E) and is therefore called a third. C to G spans five letter names (C, D, E, F, G) and is called a fifth. The quality — perfect, major, minor, augmented or diminished — describes the precise size of the interval in semitones within that numerical category. Together the number and quality give a complete description of any interval — for example a major third, a perfect fifth or a minor seventh.
Perfect Intervals
Four intervals are classified as perfect — the unison, the fourth, the fifth and the octave. Perfect intervals have a particularly stable, open sound and have been considered consonant across virtually all musical traditions and historical periods. The perfect fifth in particular is one of the most important intervals in tonal music — it forms the basis of the circle of fifths and is present in the majority of chords. A perfect interval becomes augmented if it is widened by one semitone and diminished if it is narrowed by one semitone — there is no major or minor version of a perfect interval.
The four perfect intervals — unison (0), perfect fourth (5), perfect fifth (7) and octave (12 semitones).
Major and Minor Intervals
The second, third, sixth and seventh intervals each come in major and minor versions. A major interval is one semitone wider than its minor equivalent. For example a major third spans four semitones while a minor third spans three semitones, and a major seventh spans eleven semitones while a minor seventh spans ten semitones. Major intervals tend to have a brighter, more open sound while minor intervals tend to sound darker or more tense. The distinction between major and minor thirds is particularly important because it is what determines whether a chord sounds major or minor.
Major third (4st) and minor third (3st) compared — then major seventh (11st) and minor seventh (10st).
Augmented and Diminished Intervals
Augmented intervals are one semitone wider than a perfect or major interval of the same number. Diminished intervals are one semitone narrower than a perfect or minor interval of the same number. The most commonly encountered augmented interval is the augmented fourth — also called the tritone — which spans six semitones and divides the octave exactly in half. The tritone has a highly distinctive tense and unstable sound and appears frequently in dominant seventh chords. Doubly augmented and doubly diminished intervals exist in theory but are rarely encountered in practice.
Perfect fourth (5st), tritone (6st) and perfect fifth (7st) — one semitone separates each.
The Complete Interval Table
The thirteen intervals from unison to octave, with their qualities, semitone counts and common examples from C:
| Interval | Semitones | Example from C |
|---|---|---|
| Unison | 0 | C to C |
| Minor 2nd | 1 | C to D♭ |
| Major 2nd | 2 | C to D |
| Minor 3rd | 3 | C to E♭ |
| Major 3rd | 4 | C to E |
| Perfect 4th | 5 | C to F |
| Tritone | 6 | C to F♯ |
| Perfect 5th | 7 | C to G |
| Minor 6th | 8 | C to A♭ |
| Major 6th | 9 | C to A |
| Minor 7th | 10 | C to B♭ |
| Major 7th | 11 | C to B |
| Octave | 12 | C to C |
All thirteen intervals from unison (P1) to octave (P8), built upward from C4. TT = tritone.
Simple vs Compound Intervals
A simple interval is any interval of an octave or smaller — from a unison up to an octave spanning twelve semitones. A compound interval is any interval larger than an octave. Compound intervals are named by adding seven to the simple interval number — a ninth is a compound second, a tenth is a compound third, an eleventh is a compound fourth and so on. In practical music reading, compound intervals are most commonly encountered in piano music, orchestral scores and jazz harmony. For the purposes of interval training and sight reading, mastering the thirteen simple intervals from unison to octave is the primary goal.
Ascending and Descending Intervals
An ascending interval moves from a lower note to a higher note — the second note is higher in pitch than the first. A descending interval moves from a higher note to a lower note. The interval number and quality remain the same regardless of direction — a major third ascending from C to E is still a major third when played descending from E to C. However the visual appearance on the staff is different depending on direction, which is why practising both ascending and descending interval recognition is important for fluent sight reading. The Clef Trainer interval trainer includes an ascending, descending and mixed mode to help you practise both directions.
Consonant and Dissonant Intervals
Consonant intervals have a stable, resolved sound that feels complete on its own. Dissonant intervals have a tense, unstable sound that creates a sense of motion or need for resolution. The perfect intervals — unison, fourth, fifth and octave — are strongly consonant. Major and minor thirds and sixths are mildly consonant and form the basis of most pleasant sounding harmony. Minor seconds, major sevenths and the tritone are strongly dissonant and create tension that typically resolves to a consonant interval. Understanding consonance and dissonance helps musicians make sense of why chord progressions and melodies move the way they do.
Intervals on the Staff
On the staff, intervals have a clear visual pattern that experienced sight readers use instinctively. A unison or second involves two notes that are adjacent — either on the same line or space, or on a line and the immediately adjacent space. A third always skips one position — both notes sit on lines or both sit in spaces. A fourth and fifth involve a line-to-space or space-to-line relationship with varying gaps. An octave always has both notes in the same visual position — both on lines or both in spaces — but separated by the full span of the staff. Learning these visual patterns is a faster route to interval recognition than counting semitones note by note.
Intervals from E4 using natural notes — showing the line-to-space and line-to-line visual patterns across the staff.
How to Recognise Intervals by Sight
The most effective technique for interval recognition is to associate each interval with a familiar song that begins with that interval. This gives your ear and eye a concrete reference point for each interval size. Some classic associations are: major second — Happy Birthday, minor third — Smoke on the Water, major third — When the Saints Go Marching In, perfect fourth — Here Comes the Bride, perfect fifth — Star Wars theme, minor sixth — The Entertainer, major sixth — My Bonnie Lies Over the Ocean, octave — Somewhere Over the Rainbow. Building a personal set of reference songs for each interval is one of the most reliable long term memorisation strategies.
How to Practice Interval Recognition
Begin with the five most common intervals — major second, minor third, major third, perfect fourth and perfect fifth — and practise identifying them on the staff before adding the others. Use Clef Trainer's interval trainer to drill random intervals with immediate feedback, starting with ascending intervals only before switching to mixed direction mode. Aim for instant identification within two seconds per interval rather than slow calculation. Once the simple intervals feel automatic, challenge yourself with compound intervals and chromatic variations. Consistent daily practice of ten to fifteen minutes will build interval recognition speed faster than occasional longer sessions. For related note-reading practice see the treble clef and bass clef guides, and for understanding how intervals relate to key signatures see the key signatures guide.
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