Perfect intervals have their own naming group. Major and minor intervals come in pairs, with the minor version one semitone narrower than the major version. That one-note change affects the sound of many chords and melodies, but the result still depends on context.
Four interval numbers come in major/minor pairs: 2nds, 3rds, 6ths, and 7ths. Each pair is just one semitone apart, so moving the upper note by one key changes the quality.
2nds - the step intervals
The smallest named intervals (besides unison). You already know these as semitones and tones from the Notes & Pitch topic. Tap each to hear the difference.
Minor 2nd (1 semitone)
Tense, clashing - think Jaws theme
Major 2nd (2 semitones)
Neutral, stepping - a gentle walk up
m2 (C-Db = 1 semitone) vs M2 (C-D = 2 semitones)
3rds - the emotion intervals
The 3rd often determines whether a triad is major or minor. Lowering the upper note by one semitone changes C-E into C-Eb, so the 3rd is a useful place to listen when comparing chord quality.
Minor 3rd (3 semitones)
Three semitones above the root
Major 3rd (4 semitones)
Four semitones above the root
This is exactly the interval that separates a major chord from a minor chord. C major has C-E (major 3rd), C minor has C-Eb (minor 3rd) - one semitone is all it takes.
6ths - warm and sweet
6ths are wider intervals with a warm, lyrical quality. They're common in vocal harmonies and gentle melodies.
Minor 6th (8 semitones)
Bittersweet, yearning
Major 6th (9 semitones)
Warm, nostalgic, sweet
7ths - tension and colour
7ths sit just below the octave - close enough to create tension. Adding a 7th to a chord is what turns a plain triad into a richer seventh chord.
Minor 7th (10 semitones)
Bluesy, edgy, dominant
Major 7th (11 semitones)
Dreamy, jazzy, shimmering
The pattern
For 2nds, 3rds, 6ths, and 7ths, the minor form is one semitone smaller than the major form. That changes the interval's sound, but it does not impose one fixed mood outside its melody, register, rhythm, and harmony.
Try it
Choose one pair, such as C-Eb and C-E. Predict which note is one semitone higher, play both, and describe how the colour changes. Repeat with the 6th or 7th pair from the table.
Your check is simple: for these interval families, the major version is one semitone larger than the minor version.
Key takeaway
2nds, 3rds, 6ths, and 7ths each come in major and minor versions, one semitone apart. The 3rd strongly affects the quality of a major or minor chord, while a 7th changes the interval content and often affects its pull toward another chord tone.
Next: the strangest interval of all - the tritone, plus how intervals can be augmented or diminished.
Major vs minor in action
Generate chords in Starts - switch between major and minor keys to hear the 3rd flip.