Table of Contents
A chord is any combination of three or more pitch classes that sound simultaneously. A three-note chord whose pitch classes can be arranged as thirds is called a triad. To quickly determine whether a three-note chord is a triad, arrange the three notes on the “circle of thirds” below. The pitch classes of a triad will always sit next to each other. Identifying and labeling triads Triads are identified according to their root and quality.
To find a triad’s root, arrange the pitch classes on a circle of thirds (mentally or on paper). The root is the lowest in the three-pitch-class clump. Expressed another way, if the circle ascends by thirds as it moves clockwise, the root is the “earliest” note (thinking like a literal clock), and the other pitch classes come “later.”
Oance you know the root, you can identify the remaining notes as the third of the chord (a third above the root) and the fifth of the chord (a fifth above the root).
To find a triad’s quality, identify the interval between the root and the other members of the chord. There are four qualities of triads that appear in major and minor scales, each with their own characteristic intervals.
- major triad: M3 and P5 above the root (as in do–mi–sol)
- minor triad: m3 and P5 above the root (as in do–me–solor la–do–mi)
- diminished triad: m3 and d5 above the root (as in ti–re–fa)
- augmented triad: M3 and A5 above the root (as in me–sol–ti)
A triad can be summed up by a single symbol, such as a lead-sheet chord symbol. A lead sheet symbol includes information about both root quality, as well as which pitch class occurs in the lowest voice (called the bass regardless of who is singing or playing that pitch).
A lead-sheet symbol begins with a capital letter (and, if necessary, an accidental) denoting the root of the chord. That letter is followed by information about a chord’s quality:
- major triad: no quality symbol is added
- minor triad: lower-case “m”
- diminished triad: lower-case “dim” or a degree sign “°”
- augmented triad: lower-case “aug” or a plus sign “+”
Finally, if a pitch class other than the chord root is the lowest note in the chord, a slash is added, followed by a capital letter denoting the pitch class in the bass (lowest) voice.
A C-major triad’s lead-sheet symbol is simply C. A C-minor triad is Cm. A D-sharp-diminished triad with an F-sharp in the bass is D#dim/F#. And so on.
Chords are often labeled according to their function within a key. One system for doing so uses Roman numerals to designate the scale degree of the chord’s root. Some musicians also use Roman numerals to describe the quality of the chord. Capital Roman numerals (I, II, III, etc.) are used for major triads. Lower-case Roman numerals (i, ii, iii, etc.) are used for minor triads. Lower-case Roman numerals followed by a º sign (iiº, viiº, etc.) are used for diminished triads. Capital Roman numerals followed by a + sign (V+, for example) are used for augmented triads. In general, Roman numerals are generally labeled below the score.
(Some musicians prefer to use Roman numerals only to reflect the scale-degree of the chord root. In such cases, all Roman numerals are capital. In this textbook, we use all-capital Roman numerals to refer to chords generally, when quality does not matter. When notating specific chords with specific qualities, we will differentiate those qualities in the Roman numerals.)
In major keys, chords with the same Roman numeral are made up of the same scale-degrees (using the same solfège syllables), and they have the same quality. In other words, triads labeled “I” in any major key will be major triads containing do, mi, and sol. iii triads will be minor triads containing mi, sol, and ti, etc. The same is true for minor keys (though I in minor is different from I in major).
Types of triads: I (help·info), i (help·info), io (help·info), I+ (help·info)
In music, a triad is a set of three notes (or “pitches”) that can be stacked vertically in thirds. The term “harmonic triad” was coined by Johannes Lippius in his Synopsis musicae novae (1612).
When stacked in thirds, notes produce triadic chords. The triad’s members, from lowest-pitched tone to highest, are called:
- the root
- 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). Perfect fifths are the most commonly used interval above the root in Western classical, popular and traditional music.
(Note: The notes of a triad do not have to use the root as the lowest note of the chord, due to the principle of inversion. A triad can also use the third or fifth as the lowest note of the chord. Inverting a chord does not change the root note.)
Some twentieth-century theorists, notably Howard Hanson and Carlton Gamer, expand the term to refer to any combination of three different pitches, regardless of the intervals amongst them. The word used by other theorists for this more general concept is “trichord”. Others, notably Allen Forte, use the term to refer to combinations apparently stacked of other intervals, as in “quartal triad”.
In the late Renaissance music era, and especially during the Baroque music era (1600–1750), Western art music shifted from a more “horizontal” contrapuntalapproach (in which multiple, independent melody lines were interwoven) toward chord progressions, which are sequences of chords. The chord progression approach, which was the foundation of the Baroque-era basso continuo accompaniment, required a more “vertical” approach, thus relying more heavily on the triad as the basic building block of functional harmony.
Each triad found in a diatonic (single-scale-based) key corresponds to a particular diatonic function. Functional harmony tends to rely heavily on the primary triads: triads built on the tonic, subdominant (typically the ii or IV chord), and dominant (typically the V chord) degrees. The roots of these triads begin on the first, fourth, and fifth degrees (respectively) of the diatonic scale, otherwise symbolized: I, IV, and V (respectively).
Primary triads, “express function clearly and unambiguously. The other triads of the diatonic key include the supertonic, mediant, submediant, and subtonic, whose roots begin on the second, third, sixth, and seventh degrees (respectively) of the diatonic scale, otherwise symbolized: ii, iii, vi, and viio (respectively). They function as auxiliary or supportive triads to the primary triads.
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