Perfect intervals are stable and neutral. Major and minor intervals are where emotion lives. Major intervals sound bright, minor intervals sound dark - same recipe, just swapping sugar for bitters.
Four interval numbers come in major/minor pairs: 2nds, 3rds, 6ths, and 7ths. Each pair is just one semitone apart - the narrowest possible ingredient swap.
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 is the interval that defines whether a chord sounds happy or sad. It's the single most important interval in Western harmony.
Minor 3rd (3 semitones)
Dark, sad, introspective
Major 3rd (4 semitones)
Bright, happy, confident
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
Notice the rule: minor is always one semitone smaller than major. That single semitone difference flips the mood every time.
Key takeaway
2nds, 3rds, 6ths, and 7ths each come in major (bright) and minor (dark) versions, always one semitone apart. The 3rd is the most important - it defines whether chords and scales sound happy or sad. The 7th adds tension and richness.
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.