The major triad is composed of a stacked major third plus minor third. The two commonest ways it appears in diatonic harmony are as chord I in a major key (do-mi-sol), and chord V (sol-ti-re) in major and minor keys. It’s also very common for it to appear as chord IV in major keys (fa-la-do).
The minor triad is composed of a stacked minor third plus major third. It also occurs within the diatonic scale. In minor keys, it appears most commonly as chord i (do-me-sol). In major keys, it appears commonly as chord ii (re-fa-la) and as chord vi (la-do-mi).
The diminished triad is composed of two stacked minor thirds. It functions as chord vii0 in both major and minor keys, as well as chord ii0 in minor keys.
The augmented triad is composed of two stacked major thirds. It is relatively rare in diatonic harmony. When it does occur, it is often spelled sol-ti-ri and appears as a chromatic variant of the dominant (sol-ti-re).
It is easy to identify the chord quality of triads if you listen carefully. Hearing the inversion is a little harder for compound triads than for simple triads, but the trick is to identify the root of the chord and relate it to the bass note. You may also wish to consider an imaginary context for root movement and voice-leading.
Procedure
Doubling Rules
All exam questions will conform to the rules of good voice-leading, especially the rules for doubling. Please review and memorize the rules:
Review the following playlists to re-familiarize yourself with the styles and contexts of the different triads and inversions.