Triad
A triad is a chord composed of three tones. Triads composed of roots, thirds and fifths are fundamental elements of tonal music. A tonic triad usually appears at the start and end of a piece, and most harmonic movement within tonal music is comprised of progressions through various triads.
Contents
Components
The three tones traditionally present in a triad are the root, a third, and a fifth. These triads are referred to as tertian because they consist of stacked thirds. A major triad on the root C (a C major chord) would then include the notes C, E, and G. The root would be the C, the third E, and the fifth G.
Root
The root is the fundamental tone of any triad. Without a root, it can be difficult to identify a triad. For example, the two tones A and C can belong to either an F major without the root or A minor without the fifth. Another example would be the tones F and A, which can belong to F major or D minor.
Fifth
The fifth is built upon the root and outlines the triad: without a fifth, two tones can be reinterpreted in the same way as a triad without a root, referring to the above stated predicament. The fifth can exist in three positions, perfect, diminished, and augmented. Here, we have the perfect fifth that outlines some kind of G triad:
Third
The third is built between the root and the fifth and in most cases defines the quality of the chord. Notable exceptions are diminished and augmented chords where the fifth also defines the quality of the chord. In the overwhelming majority of cases, the third is major or minor. Here, we have G major and G minor. Note that the quality of the chord is determined by the quality of the third, in this case B or B-flat.
Triad qualities
The majority of triads that occur in tonal music can be categorized into one of four types, according to the quality of the intervals present in the chord:
| Quality | Interval construction | Abbreviation |
| Major | M3, m3 | M, Maj, +, ▲, or nothing at all |
| Minor | m3, M3 | m, min, or - |
| Diminished | m3, m3 | dim or ° |
| Augmented | M3, M3 | aug or + |
Major triad
The major triad is built with a major third and a perfect fifth from the root. It is stable and consonant, and is generally associated with the major mode. Here, a major triad is built on Eb : the perfect fifth is Bb and the major third is G.
Minor triad
The minor triad is built with a minor third and a perfect fifth from the root. It is slightly less stable than the major triad, and is associated with the minor mode. Here, a minor triad is built on F#: the minor third is A, and the perfect fifth is C#:
Diminished triad
The diminished triad is built with a minor third and diminished fifth from the root. It is dissonant and unstable. Here, a diminished triad is built on C: the minor third is Eb, and the diminished fifth is Gb:
Augmented triad
The augmented triad is built with a major third and an augmented fifth from the root. It generally appears in the minor mode when using the raised forms of the sixth and seventh scale degrees. Here, an augmented triad is built on F: the major third is A, and the augmented fifth is C#:
Inversions of tonal-context triads
A triad can be in three different positions, depending on whether the root, third, or fifth is the lowest tone.
Root position (5/3)
A triad is in root position when the root is the lowest chord tone (in the bass). In this position, the third and fifth are vertically stacked "on top" of the root. Figured bass notation identifies this as 5/3. Because of its close correlation with the overtone series, the root position is the most stable position of a major or minor triad. Below are triads in root position (or 5/3 position):
<music>\cadenzaOn \meterOff <c e g>1 <bes' des fes> \clef bass <d,, f a> <g, d' b'> \clef alto <g' b d>1 </music>
First inversion (sixth chord, 6/3)
A triad is in first inversion when the third is in the bass. The fifth and root are vertically stacked "on top" of the third. Figured bass notation identifies this as 6/3 position, and some reference first inversion as a "sixth chord", owing to the presence of a sixth instead of a fifth (however, this interpretation is a part of voice-leading and is of little concern for the moment). The 6/3 position is often used to provide variety, or connect two root-position triads (two inversions of the same triad can also be connected). It sounds somewhat less stable than the root position. Below is a triad first in root position, then in first inversion (or 6/3 position):
<music>\cadenzaOn \meterOff <g' bes d>1 <bes d g>1 \clef bass <bes,, d g>1 \clef alto <bes' d g>1 </music>
Second Inversion (6/4)
A triad is in second inversion when the fifth is in the bass. The root and third are vertically stacked "on top" of the fifth. Figured bass notation identifies this as 6/4 position. The 6/4 position is the least stable. This is because of the nature of overtones and the fact that the fifth when in the base tends to exert itself to the point that it wants to "resolve" into a chord with the fifth as a new fundamental. As such, this position is often employed in cadences. Below is a triad first in root position, then in second inversion (or 6/4 position):
<music>\cadenzaOn \meterOff <f a c>1 <c f a >1 \clef bass <c, f a>1 \clef alto <c' f a>1 </music>
Octave displacement
Triads often appear where the bass is separated by a distance of an octave, or more, from the other chord tones. However, this does not affect the position of the triad (the position is always determined by the lowest chord tone, the bass). In both the following examples, a triad is in root position:
<music> <d f' a>1 <a e' c'>1 </music>
Identification and notation of tonal-context triads
Identification
A triad is identified using two elements: the root of the triad, and the quality of the triad itself. Thus, a major triad on G would be identified as G Major. An augmented triad on F would be identified as F Augmented.
To identify a triad, one must first determine the root. In the example below, we have three notes present: G - Bb - D. By bringing the triad into root position (that is to say, where the lowest tone is the root, and the third and fifth are stacked on top of it), it becomes clear that the triad is to be identified as G. Now, one must determine the quality of the triad. In the example below, the third (G - Bb) is minor, and the fifth (G-D) is perfect, constituting a minor triad. The triad in the example is thus identified as G Minor.
<music> <d g bes>1 <g bes d>1 <g bes>1 <g d'>1 <g bes d>1 </music>
Similarly, the triad in this example has Eb as its root. The third (Eb - G) is major and the fifth (Eb - B) is augmented. The triad is thus identified as Eb Augmented.
<music> <g' b ees>1 <ees g b>1 <ees g>1 <ees b'>1 <ees g b>1 </music>
Other tonal-context triads
Mostly through voice-leading phenomena, triads can be acheived where the fifth is not perfect, diminished or augmented, and where the third is diminished or augmented. These triads are not considered independent harmonic entities, but rather a by-product of voice-leading. A brief example follows, where Dm is altered by the third, F, moving downward by chromatic movement to Eb:
<music> <d f a>1 <d fes a>1 <c ees a>1 </music>
The augmented sixth chord
A common type of triad that does not fit the previously stated criteria is the augmented sixth chord (often found in 6/3 position, hence its name). In root position, the augmented sixth chord is composed of a diminsihed fifth and dimished third. Its main function (as an independent harmonic entity) is to lead to the chord whose root corresponds to the resolution of the diminished third (often the dominant). Here, we have an augmented sixth chord on D#, first in its usual configuration, then in root position:
<music> <f a dis>1 <dis f a>1 </music>
Triads used in extra-tonal and nontonal contexts
As a triad's basic characteristics are to be composed of three tones, many triads can be built which do not respect the historic model of root-third-fifth. A basic example would be that of a triad built using quartal harmony (harmony based not on the stacking of thirds to produce chords with fifths, sevenths, etc., but rather fourths and fifths):
<music> <c f bes>1 \clef bass <a, d g>1 </music>
Other triads, often found in 20th and 21st century music, include triads built with a second displacing the third or fifth:
<music> <c e f>1 <c d g>1 \clef alto 1 1 </music>
Triads built on seconds (as independent harmony, or as part of a tone cluster) are also feasible:
<music> <d e f>1 <e fis gis>1 \clef bass <e, fis g>1 </music>
Many other types of triads are possible, using many different intervals, and as such it would be tedious and useless to list them all.
