Augmented triad

In music, an augmented triad is a triad, or chord, consisting of two major thirds (an augmented fifth). The term augmented triad arises from an augmented triad being considered a major chord whose top note (fifth) is raised, or augmented. It can be represented by the integer notation {0, 4, 8}.

Harmonic considerations

Whereas a major triad, such as C-E-G, contains a major third (C-E) then a minor third (E-G), with the interval of the fifth (C-G) being "perfect", the augmented triad sharpens that fifth (to an augmented fifth), becoming C-E-G♯. In other words the top note is raised a half step.

If an octave from the root is added, the resulting chord (C-E-G♯-C) contains also a diminished fourth (G♯-C); this is the enharmonic equivalent of a major third, so the full-octave chord is, in effect, three major thirds.

In just intonation, the interval between two major thirds and an octave, 2/(5/4)², is 32/25, which is flatter by a septimal kleisma of size 225/224 than the septimal major third with ratio 9/7. While septimal meantone temperament tempers out the septimal kleisma, some other temperaments, for example miracle temperament, do so also, and in all of these temperaments the augmented triad may be identified with a circle of two major and one septimal major thirds, making up an octave.