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The problem it solves
An interval's number (third, sixth…) doesn't tell the whole story: the major or minor quality is what decides its colour and whether a triad will be major or minor.
Detailed theory
Key idea
Same number, two sizes: the major version has one more semitone than the minor.
That single-semitone difference is what changes the colour of melodies and chords.
Understand it
An interval's number (second, third, sixth, seventh) is counted by the degrees it spans on the staff: C–E is a third because it covers C-D-E, three degrees. But that number does not fix its exact size.
The exact size is measured in semitones. A major third is four semitones (C–E); a minor third is three (C–Eb). Whenever an interval can be major or minor, the minor is one semitone smaller.
The major and minor qualities only apply to seconds, thirds, sixths and sevenths. Unisons, fourths, fifths and octaves form another family: the perfect intervals.
An analogy: the number counts the steps (from C to E there are three steps: a third); the quality, major or minor, is a single-semitone adjustment that changes its colour without changing the number.
How to recognise it
How it's written
It is written with an M or an m before the number: M3 and m3, M6 and m6. On the staff the number shows through the degrees it spans, and the accidental (a sharp or a flat) adjusts the quality.
How it feels
Compare the same third in its major and minor versions: the major sounds more open and bright, the minor more inward and dark. It is a change of colour, not of happiness or sadness.
Common mistake
Counting only the semitones and forgetting the diatonic number, that is the degrees the interval spans.
Assuming major means happy and minor sad: it is a question of colour that depends on the context.
Try it
Play C–E and then C–Eb, first separately and then together: pinpoint the semitone of difference.
From another note such as G, build the major third (G–B) and the minor (G–Bb) and confirm the relationship holds.
On the instrument
Interval distance
C–E: four semitones. The major third sounds open and bright.
Interval distance
C–Eb: three semitones, one fewer than the major. The minor third sounds more inward and dark.
Songs that start with each interval
- Minor 2ndTauró (Jaws)
- Major 2ndGermà Jaume (Frère Jacques)
- Minor 3rdGreensleeves
- Major 3rdWhen the Saints Go Marching In
Contrast minor and major openings of famous songs: the minor versions (Jaws, Greensleeves) sound more inward; the major ones (Frère Jacques, When the Saints) more open and bright.
Where it's used
- Recognising chords
- Hearing whether the third of a chord is major or minor.
- Singing melodies
- Anticipating the colour of a leap before making it.
- Building from any note
- Constructing scales, chords and melodies from any starting note.
- Training the ear
- Training the ear to recognise distances and colours.
Examples
Staff & keyboard
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Encadena dues terceres: C→E és una tercera major (4 semitons) i E→G una de menor (3 semitons). Escolta-les seguides al pentagrama i al teclat.
Exercises
Major or minor — basic
Ascending thirds only: decide whether they sound major or minor.
Complete 5 attempts · 70% accuracy to pass
Major or minor — intermediate
Seconds, thirds and sixths in both directions: pick Major or Minor.
Complete 8 attempts · 70% accuracy to pass
Major or minor — advanced
Seconds, thirds, sixths and sevenths in both directions: pick Major or Minor.
Complete 10 attempts · 70% accuracy to pass
Mini test
Check that you've got it.
0/8 answeredQuestion 1/8
What sets a major third apart from a minor third?