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The problem it solves
The augmented triad gives you a suspended, mysterious colour that no major or minor chord can: it is used to create tension, ambiguity and chromatic transitions with no clear centre.
Detailed theory
Key idea
It is stacked from TWO major thirds in a row (4 + 4 semitones): that is why the fifth becomes augmented.
Between the root and the fifth there is an augmented fifth (8 semitones), an interval that sounds unstable and floating.
Understand it
Start from a root and add a major third (four semitones) above it: that is the third of the chord. Then add another major third (four more semitones): that is the augmented fifth. So the augmented triad stacks two equal major thirds.
In C: C (root), E (major third over C) and G# (major third over E). From C to G# there are eight semitones, an augmented fifth: a semitone higher than the perfect fifth of the major triad.
This symmetry has an important consequence: the augmented triad splits the octave into three exactly equal major thirds (C-E-G#-C). Since all the distances are identical, no note stands out as a clear root and the tonal centre stays ambiguous.
It is not native to the major scale; it appears on the third degree of the harmonic minor scale (III+) and, in general, it is used occasionally to add colour, create tension or link chords with chromatic motion, not as a resting point.
An analogy: if the major triad is a firmly planted tower, the augmented one is a perfectly regular spiral staircase that keeps turning without ever reaching a landing: every step (the thirds) is the same, so you never quite know where the floor is.
Stacked triad
The only difference from the major triad is the fifth: C major has G (perfect fifth); C augmented raises this note to G#.
How to recognise it
How it's written
In American chord symbols it is written with the + symbol or the abbreviation aug after the root letter: C+ or Caug mean C augmented. On the staff it is recognised by the fifth raised with a sharp (G# instead of G).
How it feels
It sounds open, suspended and restless: a kind of mysterious floating that begs to resolve to another chord. It sounds neither clearly happy nor sad, but ambiguous and unfinished.
Common mistake
Confusing the augmented fifth (8 semitones) with the perfect fifth (7 semitones): the only difference from the major triad is that the fifth goes up a semitone.
Thinking it is a stable resting chord: because of its symmetry it is unstable and usually works as a passing chord or tension toward another chord.
Try it
Play C-E-G (major triad) and then raise the G to G#: you will hear how the stable chord turns suspended and floating.
Play C-E-G# as an arpeggio and notice that the two distances (C-E and E-G#) sound exactly the same: they are two major thirds.
On the instrument
Stacked triad
C augmented: two major thirds stacked (C-E and E-G#, 4 semitones each). The fifth becomes augmented.
Interval distance
From C to G# there are 8 semitones: an augmented fifth, a semitone wider than the perfect fifth.
Where it's used
- Adding tension and colour
- Introducing a suspended, mysterious chord that no major or minor triad can offer.
- Linking chords chromatically
- Using the augmented fifth as a passing note to connect two chords with smooth motion.
- Recognising the augmented quality
- Telling an augmented triad by ear from its floating, restless sonority.
Examples
Stacked triad
C augmented (C-E-G#) sounding as a block and as an arpeggio: the suspended, floating sound of the two major thirds.
Prepares you for
Exercises
Play augmented triads — basic
Play the augmented triad shown, with simple roots (C, G, F).
Complete 5 attempts · 70% accuracy to pass
Play augmented triads — intermediate
Play the augmented triad shown, now with more roots (includes Bb).
Complete 8 attempts · 70% accuracy to pass
Play augmented triads — advanced
Play the augmented 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 an augmented triad?