The minor 3rd and major 3rd differ by one semitone: a minor 3rd spans three semitones and a major 3rd spans four. C to Eb is a minor 3rd and C to E is a major 3rd, and that single semitone decides whether a chord is minor or major.
What is the difference between a minor 3rd and a major 3rd?
The minor 3rd and the major 3rd are the most important pair of intervals in music, because the 3rd is the note that decides whether a chord is major or minor. A minor 3rd spans three semitones and a major 3rd spans four, and the difference is exactly one semitone. C to Eb is a minor 3rd, three semitones; C to E is a major 3rd, four semitones. Both intervals span three letter names, which is why both are 3rds, and the semitone count is what decides the quality. The emotional difference between the two 3rds is the most reliable in all of music theory. The major 3rd sounds bright, warm and cheerful, while the minor 3rd sounds dark, sad and introspective, and most listeners can hear the difference immediately, even without training. That is why the 3rd is the first interval a beginner learns to recognise, and why composers use it to set the mood of a piece: change the 3rd and you change the feeling, even if every other note stays the same.
How the two 3rds compare
Count them the same way as any interval: letters first, then semitones. A to C is three letters, A, B, C, and three semitones, so it is a minor 3rd. A to C# is three letters and four semitones, so it is a major 3rd. E to G is a minor 3rd, three semitones, while E to G# is a major 3rd, four semitones. The pattern holds on every root: the minor 3rd is always the note three semitones above the root, and the major 3rd is always the note four semitones above it, which is the 3rd degree of the major scale. The 3rds appear in every chord and every scale. A major chord has a major 3rd and a minor chord has a minor 3rd; a major scale has a major 3rd above its root and a natural minor scale has a minor 3rd. The dorian mode has a minor 3rd but a major 6th, which is part of its distinctive sound, and the mixolydian mode has a major 3rd but a minor 7th. The C major guitar chord and the C minor guitar chord show the two 3rds deciding the chord quality, and the interval calculator measures either 3rd from any root.
Worked example — 3rds above G. G to Bb is three letters, G, A, B, and three semitones, so it is a minor 3rd. In the sharp-only system used by ChordFlow, Bb is spelled A#, and G to A# is also a minor 3rd, three semitones, with the same three letters. G to B is three letters and four semitones, so it is a major 3rd, and B is the 3rd degree of the G major scale. Play G and A# together and listen for the dark, narrow sound, then play G and B together and notice the brightness opening up. The G major scale shows the major 3rd, B, as its 3rd degree.
How to practise hearing the 3rds
Practise the 3rds as a pair, major then minor, on the same root, so your ear learns the one-semitone difference as a single, vivid sound.
- Play C and E together, a major 3rd, then C and Eb together, a minor 3rd, and listen for the brightness giving way to darkness.
- Sing a major 3rd above a root note, then lower the top note by a semitone to sing the minor 3rd, checking yourself against the piano.
- Play the C major guitar chord and the C minor guitar chord back to back, and notice that only the middle note changes.
- Find the 3rd in every chord of the key of C major, and name whether each one is major or minor before you check.
- Use the interval calculator to quiz yourself on 3rds from random roots until you can name the quality from the sound alone.
Common mistakes
- Thinking the 3rd is the least important note — The 3rd is the most important note after the root, because it decides whether a chord is major or minor. Leaving it out, or playing it wrong, changes the chord completely, while leaving out the 5th barely matters.
- Counting the 3rd as two semitones — A minor 3rd is three semitones, not two, and a major 3rd is four, not three. Counting the steps between the notes instead of the semitones gives the wrong answer, so count the semitones carefully.
- Confusing the minor 3rd with the augmented 2nd — C to Eb is a minor 3rd, three semitones across three letters, while C to D# is an augmented 2nd, three semitones across two letters. They sound identical, but the letter count makes them different intervals with different functions.
Quick reference
This table lists the minor and major 3rds above six roots, so you can see the one-semitone difference working on the roots you will meet most often. In every row the minor 3rd is the note three semitones above the root and the major 3rd is the note four semitones above it, and the letter count is three in both columns.
| Root | Minor 3rd (3 semitones) | Major 3rd (4 semitones) |
|---|---|---|
| C | D# | E |
| G | A# | B |
| D | F | F# |
| A | C | C# |
| E | G | G# |
| F | G# | A |
Play each row on piano as a pair, minor 3rd first and major 3rd second, and listen for the darkness giving way to brightness as the top note rises by one semitone. When the pairs feel familiar, build the major and minor triads on each root, and notice that the 3rd is the only note that changes between the two chords.
Frequently asked questions
What is a minor 3rd?
A minor 3rd is an interval of three semitones between two notes three letters apart, such as C to Eb or A to C. It is the interval that makes a chord minor, and it sounds dark and sad.
What is a major 3rd?
A major 3rd is an interval of four semitones between two notes three letters apart, such as C to E or G to B. It is the interval that makes a chord major, and it sounds bright and cheerful.
Why is the 3rd so important?
Because the 3rd decides whether a chord is major or minor, and whether a scale is major or minor. The root names the chord and the 5th stabilises it, but the 3rd gives it its emotional character, which is why it is the first interval to learn.
How do I tell a minor 3rd from a major 3rd by ear?
Listen for the mood: the major 3rd sounds bright and open, while the minor 3rd sounds dark and narrow. Practise the pair together on the same root, major first and then minor, until the one-semitone difference is obvious.
Do 3rds appear in scales as well as chords?
Yes. A major scale has a major 3rd above its root, a natural minor scale has a minor 3rd, and the modes mix the two: dorian has a minor 3rd with a major 6th, and mixolydian has a major 3rd with a minor 7th.