An augmented chord is a tense, dreamy triad built by stacking two major thirds, which gives it a raised, or augmented, fifth. It sounds restless and unresolved, as if it wants to move somewhere, and that colour is exactly what makes it useful. It is also unusually symmetrical, which sets it apart from the other triads. Here is how an augmented chord is put together, why it sounds the way it does, and how it is used, worked out from C.
Real theory, explained plainly. It works the same on a piano, a guitar, or in a piano roll, in any key and any style. Nothing here needs a particular instrument.
An augmented chord is a triad with a raised fifth, built by stacking two major thirds. Its plain form is the augmented triad: a root, a major third and an augmented fifth, which is a perfect fifth pushed out by a semitone.
Start on any note, the root. Go up a major third, four semitones, to the second note, then up another major third from there to the third note. From C that is C up to E, then E up to G#, giving Caug = C E G#. It is often written C+ or Caug. Because it is two major thirds stacked, the outer interval, from C to G#, comes out as an augmented fifth, eight semitones wide, one semitone wider than the perfect fifth that anchors a major or minor chord.
That widened fifth is the whole story. A plain triad in its major or minor form is anchored by a stable perfect fifth, and it sits still. Push that fifth out by a semitone and the same three-note shape turns tense and unsettled, as if it is leaning toward another chord rather than resting.
You build an augmented chord by stacking two major thirds. Start on the root, go up a major third to the second note, then up another major third to the third note. A major third is four semitones, so from C you get C up to E, then E up to G#, giving Caug = C E G#. The interval from C to E is a major third, E to G# is another major third, and the outer interval from C to G# is an augmented fifth, eight semitones, the raised fifth the name points to.
Because both thirds are the same size, an augmented chord is perfectly symmetrical: it splits the octave into three equal steps, a major third each. That has an odd and useful consequence. Invert the chord, moving the bottom note up an octave, and the shape you land on is another augmented triad, so C E G# reordered still spells an augmented triad, only rooted on a different note. Follow that through and the same three notes, C E G#, serve as the augmented triad on C, on E and on G# alike. In the whole twelve-note system there are really only four distinct augmented triads, and each one is shared by three different roots.
It helps to see the augmented triad next to the other three, all worked from C. Every triad has a root, a third and a fifth; what changes is the size of the third and the size of the fifth.
| Triad | Stacked thirds | Notes from C | Tends to sound |
|---|---|---|---|
| Major | Major third, then minor third | C E G | Bright and settled |
| Minor | Minor third, then major third | C Eb G | Darker and sad |
| Diminished | Minor third, then minor third | C Eb Gb | Tense and unstable |
| Augmented | Major third, then major third | C E G# | Tense and dreamlike |
Only the major and minor triads are held together by a stable perfect fifth. The diminished triad pulls that fifth in by a semitone; the augmented triad pushes it out by a semitone. In that sense the augmented chord is close to a mirror image of the tense, inward-pulling diminished chord, one stretching the fifth outward where the other squeezes it in.
An augmented chord sounds tense because its raised fifth removes the stable anchor a chord normally rests on, and because its perfect symmetry leaves it with no note that clearly feels like home. The result is restless and dreamy rather than settled.
A major or minor triad is held together by a perfect fifth, seven semitones wide, an open interval the ear reads as stable and at rest. An augmented chord widens that fifth to eight semitones, and the ear tends to hear the stretched interval as unsettled, wanting to close back down. On top of that, because the three notes are spaced evenly, a major third apart, no single one stands out as the root, so the chord seems to float rather than sit.
That even spacing also gives the augmented chord its whole-tone flavour: its notes are drawn from the whole-tone scale, a scale built only from whole steps that has the same floating, dreamlike quality. It is part of why augmented harmony can sound magical or slightly unreal.
As with the diminished chord, that restlessness is the point rather than a fault. An augmented chord sounds incomplete on its own, which is why it is almost always heading somewhere rather than sitting still.
You mostly use an augmented chord as a passing or transition chord and as a splash of colour, rather than as a chord to rest on. Its rising, unresolved quality makes it good at nudging a progression forward into the next chord. A few common moves show the idea.
Like the diminished chord, the augmented chord works best in small doses. A brief touch of it adds a striking, dreamlike colour and a strong pull onward; leaned on too hard it can start to sound vague or unmoored, so most writers treat it as a spice rather than a chord to build on.
We built ARGISH to make this quick to hear. It is a self-playing chord synth: set a key and it voices chords and whole progressions that stay in that key, so you can hear a restless augmented colour appear and then resolve into a settled chord, rather than just reading the notes on the page. It is a fast way to hear how these chords move.
It runs free in your browser to try, and installs as AU, VST3, AAX or a standalone app when you want it inside your own sessions.
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