A triad is a set of three notes (or «pitches») that can be stacked vertically in thirds.
When stacked in thirds, notes produce triadic chords. The triad’s members, from lowest-pitched tone to highest, are called:
-the third – its interval above the root being a minor third (three semitones) or a major third (four semitones)
-the fifth – its interval above the third being a minor third or a major third, hence its interval above the root being a diminished fifth (six semitones), perfect fifth (seven semitones), or augmented fifth (eight semitones).
The root tone of a triad, together with the degree of the scale to which it corresponds, primarily determines a given triad’s function. Secondarily, a triad’s function is determined by its quality: major, minor, diminished or augmented. Major and minor chords are the most commonly used chord qualities in Western classical, popular and traditional music. In standard tonal music, only major and minor chords can be used as a tonic in a song or some other piece of music. Three of these four kinds of triads are found in the major (or diatonic) scale. Major and minor triads are considered to be consonant and stable, and diminished and augmented triads are considered to be dissonant and unstable.
Inversions of Triads
A chord’s inversion describes the relationship of its bass to the other tones in the chord. For instance, a C major triad contains the tones C, E and G; its inversion is determined by which of these tones is the bottom note in the chord. A root-position chord is sometimes known as the parent chord of its inversions. For example, C is the root of a C major triad and is in the bass when the triad is in root position; the third and the fifth of the triad are sounded above the bass. In an inverted chord, the root is not in the bass (i.e., is not the lowest note). The inversions are numbered in the order their bass tones would appear in a closed root position chord (from bottom to top). Inverting a chord does not change the root note.
|In the first inversion of a C major triad (sixth chord) the bass is E – the third of the triad – with the fifth and the root stacked above it (the root now shifted an octave higher), forming the intervals of a minor third and a minor sixth above the inverted bass of E, respectively. Major (6):|
|In the second inversion (six-four triad) the bass is G – the fifth of the triad – with the root and the third above it (both again shifted an octave higher), forming a fourth and a sixth above the (inverted) bass of G, respectively. Major (64):|
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