Chord Identification

Triads

In music, a triad is a set of three notes (or "pitch classes") that can be stacked vertically in thirds.^[1] The term "harmonic triad" was coined by Johannes Lippius in his Synopsis musicae novae (1612). Triads are the most common chords in Western music.

In the late Renaissance music era, and especially during the Baroque music era (1600–1750), Western art music shifted from a more "horizontal" contrapuntal approach (in which multiple, independent melody lines were interwoven) toward progressions, which are sequences of triads. The 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.

The root of a triad, together with the degree of the scale to which it corresponds, primarily determine its function. Secondarily, a triad's function is determined by its quality: major, minor, diminished or augmented. Major and minor triads are the most commonly used triad qualities in Western classical, popular and traditional music. In standard tonal music, only major and minor triads can be used as a tonic in a song or some other piece of music. That is, a song or other vocal or instrumental piece can be in the key of C major or A minor, but a song or some other piece cannot be in the key of B diminished or F augmented (although songs or other pieces might include these triads within the triad progression, typically in a temporary, passing role). Three of these four kinds of triads are found in the major (or diatonic) scale. In popular music and 18th-century classical music, major and minor triads are considered consonant and stable, and diminished and augmented triads are considered dissonant and unstable.

Construction

Triads (or any other tertian chords) are built by superimposing every other note of a diatonic scale (e.g., standard major or minor scale). For example, a C major triad uses the notes C–E–G. This spells a triad by skipping over D and F. While the interval from each note to the one above it is a third, the quality of those thirds varies depending on the quality of the triad:

• major triads contain a major third and perfect fifth interval, symbolized: R 3 5 (or 0–4–7 as semitones) play (help·info)
• minor triads contain a minor third, and perfect fifth, symbolized: R ♭3 5 (or 0–3–7) play (help·info)
• diminished triads contain a minor third, and diminished fifth, symbolized: R ♭3 ♭5 (or 0–3–6) play (help·info)
• augmented triads contain a major third, and augmented fifth, symbolized: R 3 ♯5 (or 0–4–8) play (help·info)

The above definitions spell out the interval of each note above the root. Since triads are constructed of stacked thirds, they can be alternatively defined as follows:

• major triads contain a major third with a minor third stacked above it, e.g., in the major triad C–E–G (C major), the interval C–E is major third and E–G is a minor third.
• minor triads contain a minor third with a major third stacked above it, e.g., in the minor triad A–C–E (A minor), A–C is a minor third and C–E is a major third.
• diminished triads contain two minor thirds stacked, e.g., B–D–F (B diminished)
• augmented triads contain two major thirds stacked, e.g., D–F♯–A♯ (D augmented).

Triads appear in close or open positions. "When the three upper voices are as close together as possible, the spacing is described as close position or close harmony. [...] The other arrangements [...] are called open position or open harmony."^[5]

Chord function

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 triad), and dominant (typically the V triad) degrees.^[6] The roots of these triads are the first, fourth, and fifth degrees (respectively) of the diatonic scale, otherwise symbolized I, IV, and V. Primary triads "express function clearly and unambiguously."^[6] The other triads in diatonic keys include the supertonic, mediant, submediant, and subtonic, whose roots are the second, third, sixth, and seventh degrees (respectively) of the diatonic scale, otherwise symbolized ii, iii, vi, and vii^o. They function as auxiliary or supportive triads to the primary triads.

Seventh chord

A seventh chord is a chord consisting of a triad plus a note forming an interval of a seventh above the chord's root. When not otherwise specified, a "seventh chord" usually means a dominant seventh chord: a major triad together with a minor seventh. However, a variety of sevenths may be added to a variety of triads, resulting in many different types of seventh chords.

In its earliest usage, the seventh was introduced solely as an embellishing or nonchord tone. The seventh destabilized the triad, and allowed the composer to emphasize movement in a given direction. As time passed and the collective ear of the western world became more accustomed to dissonance, the seventh was allowed to become a part of the chord itself, and in some modern music, jazz in particular, nearly every chord is a seventh chord. Additionally, the general acceptance of equal temperament during the 19th century reduced the dissonance of some earlier forms of sevenths.

Classification

Most textbooks name these chords formally by the type of triad and type of seventh; hence, a chord consisting of a major triad and a minor seventh above the root is referred to as a major/minor seventh chord. When the triad type and seventh type are identical (i.e. they are both major, minor, or diminished), the name is shortened. For instance, a major/major seventh is generally referred to as a major seventh. This rule is not valid for augmented chords: since the augmented/augmented chord is not commonly used, the abbreviation augmented is used for augmented/minor, rather than augmented/augmented. Additionally, half-diminished stands for diminished/minor, and dominant stands for major/minor. When the type is not specified at all, the triad is assumed to be major, and the seventh is understood as a minor seventh (e.g. a "C" chord is a "C major triad", and a "C⁷" chord is a "C major/minor seventh chord", also known as a "C dominant seventh chord"). For symbols used for seventh chords, see also Popular music symbols § Seventh chords.

Types

Dominant seventh chord

A dominant seventh chord, or major-minor seventh chord is a chord composed of a root, major third, perfect fifth, and minor seventh. It can be also viewed as a major triad with an additional minor seventh. It is denoted using popular music symbols by adding a superscript "7" after the letter designating the chord root.^[1]: 77 The dominant seventh is found almost as often as the dominant triad.^[1]: 199 The chord can be represented by the integer notation {0, 4, 7, 10}.

Of all the seventh chords, perhaps the most important is the dominant seventh. It was the first seventh chord to appear regularly in classical music. The name comes from the fact that the flat seventh occurs naturally in the scale built upon the root when it functions as the dominant (i.e., the fifth degree) of some major diatonic scale.

The note G is the dominant degree of C major—its fifth note. When we arrange the notes of the C major scale in ascending pitch and use only these notes to build a seventh chord, and we start with G (not C), then the resulting chord contains the four notes G–B–D–F and is called G dominant seventh (G⁷). The note F is a minor seventh from G, and is also called the dominant seventh with respect to G.

Harmonic seventh chord

The harmonic seventh chord is a dominant seventh chord formed by a major triad plus a harmonic seventh interval.

The harmonic seventh interval is a minor seventh tuned in the 7:4 pitch ratio, one of the possible "just ratios" defined for this interval in just intonation (slightly below the width of a minor seventh as tuned in equal temperament). With just intonation on all notes of the harmonic seventh chord, the ratio between the frequencies of the pitches in the chord is 4:5:6:7. For example, a justly intuned A harmonic seventh chord in root position starting at A440 consists of the pitches 440 Hz, 550 Hz, 660 Hz, and 770 Hz.

Sometimes called a "blue note", the harmonic seventh is used by singers, through note bending on guitars, and on other instruments not restricted to equal temperament. An often heard example of the harmonic seventh chord is the last word of the modern addition to the song "Happy Birthday to You", with the lyrics, "and many more!" The harmony on the word "more" is typically sung as a harmonic seventh chord.^[2]

Frequent use of the harmonic seventh chord is one of the defining characteristics of blues and barbershop harmony; barbershoppers refer to it as "the barbershop seventh". Since barbershop music tends to be sung in just intonation, the barbershop seventh chord may be accurately termed a harmonic seventh chord. The harmonic seventh chord is also widely used in blues-flavored music. As guitars, pianos, and other equal-temperament instruments cannot play this chord, it is frequently approximated by a dominant seventh. As a result, it is often called a dominant seventh chord and written with the same symbols (such as the blues progression I⁷–V⁷–IV⁷).

Major and minor seventh chords

While the dominant seventh chord is typically built on the fifth (or dominant) degree of a major scale, the minor seventh chord is built on the second, third, or sixth degree. A minor seventh chord contains the same notes as an added sixth chord. For example, C–E♭–G–B♭ can function as both a C minor seventh and an E♭ added sixth (Id chord).

Major seventh chords are usually constructed on the first or fourth degree of a scale, (in C or G major: C–E–G–B). Due to the major seventh interval between the root and seventh (C–B, an inverted minor second), this chord can sometimes sound dissonant, depending on the voicing used. For example, Bacharach and David's Raindrops Keep Fallin' on My Head opens with a major chord followed by a major seventh in the next measure.

The major seventh is sometimes notated as Δ7 (a delta chord) or just a Δ (which has the same meaning).

Half-diminished seventh chord

A half-diminished seventh chord is a seventh chord built from the seventh degree of a major scale. It is considered "half-diminished" because a fully diminished seventh has a double-flatted (diminished) seventh, making it enharmonically the same as a major sixth. The half-diminished seventh chord uses a minor seventh over the root of a diminished triad.

Example: (in the key of C major) B–D–F–A.

Diminished seventh chord

A diminished seventh chord is made of three superimposed minor thirds (e.g., B–D–F–A♭), which is two tritones a minor third apart (e.g., B–F, D–A♭). The diminished seventh chord has been used by composers and musicians for a variety of reasons over time. Some reasons include: as a symbol of Sturm und Drang; modulation; and for characterisation. The diminished seventh chord is seen more frequently in late classical and romantic period works but is also found in Baroque and Renaissance period works, though not as frequently.

All of the elements of the diminished seventh chord can be found in the dominant seventh flat nine (7♭9) chord as seen in a comparison of the two chords.