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Chord (music)

A chord is usually thought of as containing at least three notes. However, it is possible for only two notes to serve the same function as a chord with more notes. For example, within the context of C major, the two notes F and B have the same function together as a full dominant seventh chord (see below), even though two of the notes, G and D, are missing. Such a two-note chord is called a dyad or diad (see interval for more details).

It is even possible to give the effect of a full chord with only one note sounding at a time. This is most often done by way of broken chord of arpeggios, where each note in a chord is sounded one after the other. One of the most familiar broken chord figures is Alberti bass. See: accompaniment.

Any combination of three or more notes is a chord, although during the common practice period in western music and most popular music some combinations were given more prominence than others (the tonal ones). These more frequently used chords have particular names assigned to them, from the triad, the most simple three-note chord, to far more complex chords. Below is an explanation of some of these.

Chords are often referred to by chord symbols.

Table of contents
1 The Triad
2 Seventh Chords
3 Added tone chords
4 Nonchord tones and dissonance
5 Other types of chords
6 External links

The Triad

The most commonly used chords in western music, triads are the basis of diatonic harmony, and are composed of three notes: a root note, a note which is an interval of a third above the root, and a note which is an interval of a fifth above the root.

For example, an octave of the C major scale consists of the notes: C D E F G A B C.

Fig 1. The C major scale

The triad formed using the C note as the root would consist of C (the root note of the scale), E (the third note of the scale) and G (the fifth).

Fig 2. C, E and G - The C major triad

Using the same scale (and thus, implicitly, the key of C major) a chord may be constructed using the D as the root note. This would be D (root), F (third), A (fifth).

It should be immediately apparent on hearing these two chords that they have a different quality to them: one which does not stem merely from the difference in pitch between their roots C and D. Examination at the piano keyboard will reveal that there are four semitones between the root and third of the chord on C, but only 3 semitones between the root and third of the chord on D.

The triad on C is thus called a major triad, or major chord, and the interval from C to E a major third. A minor chord, such as the triad on D, has a smaller interval from root to third called a minor third, and the chord is D minor.

A triad can be constructed on any note of the C major scale. These will all be either minor or major, with the exception of the triad on B, the leading-tone (the last note) of the scale, which is diminished. See also Mathematics of the Western music scale.

Types of triads

As well as major and minor, there can also be augmented and diminished triads. These four are referred to collectively as the quality of the chord. For instance a triad built on top of a root D in the key of C would be said to have a minor quality.

Augmented triads are composed of a major 3rd but an augmented 5th (meaning the top note has been increased by one semitone.) Diminished triads have a minor 3rd and a diminished 5th (same as a minor triad, except the top note has been lowered by a semitone.) These rules summarise the type of triads encountered so far:

Each note has a function within the chord, the note the chord is built on is called the root of the chord, the second note a third above it is called the third of the chord, and the third note a third above the second note is called the fifth of the chord. This is true of all triads, regardless of key, inversion, or quality. For example, in an F chord, F is always the root, A (sharp, natural or flat) is always the third, and C(sharp, natural, or flat) is always the fifth.

Tonal music relies upon a key to indicate the natural relationships between the major and minor chords that result from the natural diatonic relationships. For instance, in any major key, the quality of a chord built on the fifth note of the scale will be major. This is because of the constant relationship between the tonal intervals of major scale. Chords are notated by the scale degree of their root, although there are many different conventions for indicating the quality and inversion of the chord. For Example, since the first scale degree of the C major scale is the note C, a triad built on top of the note C would be called the one chord, which might be notated 1, I, or even C in which case the assumption would be made that the key signature of the particular piece of music in question would indicate to the musician what function a C major triad was playing, and that any special functioning of the chord outside of its normal diatonic function would be inferred due to context.

Chords are also said to have a function in their diatonic scale, which relates to the expected resolution of each chord within a key. The strongest form of motion has root movement by fifth, which is the characteristic sound used as finality in most music of the baroque and classical periods, and is also exploited to modulate a piece of music into a different key. The chord function for a major scale is as follows:

The spellings of the diatonic triads of the C major scale are given in the following table, along with their quality, name, and function"

I       -- C E G -- major -- C major -- tonic
ii      -- D F A -- minor -- D minor -- subdominant
iii     -- E G B -- minor -- E minor -- tonic
IV      -- F A C -- major -- F major -- subdominant
V       -- G B D -- major -- G major -- dominant
vi      -- A C E -- minor -- A minor -- tonic
vii°    -- B D F -- dim.  -- B dim   -- dominant 

There is another type of chord function, Subdominant Minor, which is reserved for non-diatonic chords, or chords that do not occur naturally in the diatonic key, and will be dealt with separately under the heading Modal Interchange.

Inverted Triads

Triads are said to be inverted when a note other than the root is the lowest note played. There are three types of inversionss, or positions, for triads.

For notation of inverted chord chord symbols see: figured bass. Various compositional techniques in classical music have made use of inversion for a variety of interesting effects.

Seventh Chords

Seventh chords may be thought of as the next natural step in composing tertian chords is to add the note a third above the fifth of the chord, or the seventh of the chord.

Types of Seventh Chords

There are 6 types of seventh chords composed of the following intervals:

Added tone chords

An added tone chord is a traditional chord with an extra "added" note, such as the added sixth. This includes chords with an added ninth, thirteenth etc, but that do not include the intervening thirds as in an extended chord.

Nonchord tones and dissonance

A nonchord tone is a dissonant or unstable tone which is not a part of the chord that is currently playing and in most cases quickly resolves to a chord tone.

Other types of chords

Chords not formed from thirds are by many different methods, often similarly for the interval used, thus a chord made from two or more fourths on top of each other, for instance CFBbEb, is quartal. Alexander Scriabin's mystic chord may be produced quartally and Aaron Copland is one of many other composers who have used quartal chords. Chords built from seconds are secundal. Polychords are two or more chords superimposed on top of one another.

For more information see: Twentieth Century Harmony: Creative Aspects and Practice by Vincent Persichetti, ISBN 0393095398.

"Power chords" are simple intervals extended in octaves, rather than true chords, and are used extensively in many kinds of rock music.

External links