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The problem it solves
The minor triad is the other half of basic harmony: it supports degrees ii, iii and vi and the minor keys. Being able to tell it from the major gives you the essential colour contrast of tonal music.
Detailed theory
Key idea
It stacks the reverse of the major: a minor third below and a major third above.
The only difference from the major triad is the third, one semitone lower; the perfect fifth stays and keeps it just as stable.
Understand it
Start from a root and add the note a minor third (three semitones) above: that is the third of the chord. On top of it put a major third (four semitones) more: that is the fifth.
In C: C (root), Eb (minor third over C) and G (major third over Eb). From C to G there is still a perfect fifth, seven semitones, which gives the chord its solidity.
This order of thirds is the reverse of the major triad: there the major was below and the minor above. That is why the minor and major triads share root and fifth and differ only in the third.
That difference is a single semitone: lower the third of C-E-G (E) to Eb and you get C-Eb-G. That semitone shifts the colour of the chord toward something darker and more inward, but since the perfect fifth stays, it still sounds stable.
An analogy: it is the same block tower as the major (same root and fifth), but with the middle block a little lower. The piece of furniture stands just as firm; only its colour has changed.
Stacked triad
C major (C-E-G): the same root and fifth, with the third one semitone higher. Compared with C minor it shows that the whole difference is the third.
How to recognise it
How it's written
It is written by stacking 1-b3-5 over the root, for example C-Eb-G. In chord symbols you add a lowercase m or a dash to the root letter: Cm or C- mean C minor.
How it feels
It sounds stable but with a darker, more inward colour than the major. It does not necessarily mean sad; the same triad can sound serene, grave or intimate depending on context.
Common mistake
Confusing the minor triad with the major: the only difference is the third, one semitone up or down.
Thinking the minor triad is unstable: the perfect fifth keeps it as firm as the major; what changes is the colour, not the stability.
Try it
Play C-E-G and then lower the third (E) one semitone to Eb: you have just gone from C major to C minor (C-Eb-G).
Build A minor (A-C-E) and D minor (D-F-A) and notice that in all of them the third is the note that gives the minor colour.
On the instrument
Stacked triad
C minor: a minor third from C to Eb (3 semitones) and a major third from Eb to G (4 semitones), with a perfect fifth between C and G.
Interval distance
C-Eb: the minor third (3 semitones) that gives the chord its darker colour. It is the feature that sets it apart from the major triad.
Where it's used
- Tonal contrast
- Using minor chords to create emotional nuance and points of introspection in a composition.
- Harmonising degrees
- Recognising and playing the chords of the second (ii), third (iii) and sixth (vi) degrees of the key.
- Telling it from the major
- Hearing and seeing that lowering the third one semitone turns a major triad into a minor one.
Examples
Stacked triad
A minor (A-C-E): the minor triad from another root. Play it as an arpeggio and as a chord.
Exercises
Play minor triads — basic
Play the minor triad shown, with simple roots (C, G, F).
Complete 5 attempts · 70% accuracy to pass
Play minor triads — intermediate
Play the minor triad shown, now with more roots (includes Bb).
Complete 8 attempts · 70% accuracy to pass
Play minor triads — advanced
Play the minor triad shown from any of the 12 roots, including notes with accidentals.
Complete 10 attempts · 70% accuracy to pass
Mini test
Check that you've got it.
0/8 answeredQuestion 1/8
Which three notes make up a minor triad?