Note Intervals

What Is a Note Interval?

An interval is the measured distance between two pitches. When musicians say "a major third" or "a perfect fifth", they're describing how far apart two notes are — not just vaguely, but with an exact count of semitones.

A semitone (also called a half step) is the smallest interval in standard Western music. On a piano it's one key to the adjacent key, including blacks. On a guitar it's one fret. Every interval is simply a count of how many semitones separate two notes.

Intervals are the DNA of music theory. You cannot understand chords without them — a major triad is defined as "a major third plus a minor third", and that description is meaningless unless you know what those intervals are. The same is true for scales, modes, chord progressions, and voice leading. Intervals come first.

Intervals can be played harmonically (both notes at the same time, like a chord) or melodically (notes played one after another, like a melody). The interval distance is identical either way — only the context changes.

The 12 Intervals — From Unison to Octave

Within a single octave there are 13 distinct interval positions (including both endpoints), giving us 12 interval sizes. Each has a specific name, abbreviation, and character.

Interval Quality — Perfect, Major, Minor, Diminished, Augmented

Every interval has two components: a number (second, third, fourth…) and a quality (major, minor, perfect…). The number tells you how many letter names are spanned. The quality tells you the exact size in semitones.

The practical rule: perfect intervals don't have major/minor versions, and major/minor intervals don't have a perfect version. When you alter a perfect interval up or down by a semitone, it becomes augmented or diminished. When you alter a major interval down a semitone, it becomes minor.

Consonance and Dissonance

Intervals are often described as either consonant (stable, pleasant, at rest) or dissonant (tense, unstable, wanting to move). This isn't a value judgement — dissonance creates forward motion in music. Without it, everything would feel static.

Intervals Build Every Chord

Every chord type is defined by its interval recipe — the specific semitone gaps stacked from the root. Once you memorise the interval names, chord construction becomes formulaic rather than something you have to remember note-by-note.

See the pattern? Every chord is just a stack of thirds — alternating or matching major and minor thirds. Understanding this is what separates people who memorise chord shapes from people who understand harmony. The former hits a wall; the latter can construct any chord anywhere on any instrument.

Compound Intervals — Beyond the Octave

Intervals larger than an octave are called compound intervals. They work by adding 7 to the simple interval number:

• 9th = octave + major/minor second (2 semitones above the octave for M9, 1 for m9)
• 11th = octave + perfect/augmented fourth
• 13th = octave + major/minor sixth

These names show up constantly in jazz and extended harmony — a Cmaj13 chord, for instance, contains a major 13th interval (equivalent to a major 6th an octave higher). The interval logic is identical; only the register changes.

Intervals and Scale Construction

Scales are nothing more than a specific sequence of intervals stacked from a root note. The major scale uses the interval pattern: W W H W W W H (whole step, whole step, half step, whole step, whole step, whole step, half step) — or in semitones: 2, 2, 1, 2, 2, 2, 1.

Change that interval sequence and you change the scale. The natural minor scale uses: 2, 1, 2, 2, 1, 2, 2. The pentatonic scale removes two intervals entirely, leaving five notes. Every scale identity comes down to its interval sequence — nothing more.

Training Your Ear to Hear Intervals

Interval recognition by ear is one of the most practical skills in music. When you can hear "that's a perfect fifth" or "that's a major third", you can transcribe music, recognise chord qualities instantly, and tune by ear.

The classic method is to associate each interval with the opening notes of a well-known song:

• Minor 2nd — Jaws theme (da-DUM)
• Major 2nd — Happy Birthday (first two notes)
• Minor 3rd — Smoke on the Water riff (first two notes)
• Major 3rd — When the Saints Go Marching In
• Perfect 4th — Here Comes the Bride
• Tritone — The Simpsons theme
• Perfect 5th — Star Wars main theme
• Major 6th — My Bonnie Lies Over the Ocean
• Minor 7th — Somewhere (from West Side Story)
• Major 7th — Take On Me (the synth riff)
• Octave — Somewhere Over the Rainbow

Enharmonic Equivalents

Two intervals can have the same number of semitones but different names. These are called enharmonic equivalents. The tritone is the most famous example — it can be written as either an augmented 4th (C to F#) or a diminished 5th (C to G♭). Both span 6 semitones. The name you use depends on the key context and how the interval resolves.

This matters when reading or writing music notation, but for practical chord building on guitar or piano, the enharmonic name rarely changes what you actually play.