Chord (music)
In music and music theory a chord (from the middle English cord, short for accord) is three or more notes sounding simultaneously, or near simultaneously over a period of time. Broadly, 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. Thus in common usage a chord is only those groups of three notes which are tonal or have diatonic functionality.A chord is then also only the harmonic function of the group of three notes, and it is unnecessary to have all three notes form a simultaneity. Less than three notes may and often do function, in context, as a simultaneity of all notes of chord. One example is a power chord, another is a broken chord or arpeggio, 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.
Definition and Construction of Chords
Chords are named for how many notes they contain and more commonly for what type of intervalss they are constructed from.
The easiest way to name a chord, or limit its construction, is according to the number of notes included. The simplest and possibly most common chords are trichords, meaning they have three ("tri") notes, four notes being a tetrachord, six a hexachord, etc.
It is more informative to label a chord based on what type of intervals it contains, rather than how many notes, because no matter how many notes a similar interval apart you stack on top of each other, the chord still retains a characteristic sound. The most commonly discussed chords are those with notes a third apart, called tertian chords. Chords constructed from seconds are secundal, and from fourths are quartal.
Chords are labelled with chord symbols.
The triad
The most commonly used chords in western music, triadss are the basis of diatonic harmony, and are tertian trichords. That is, they are composed of three notes: a root note, a note which is a third above the root, and a note which is an interval of a fifth above the root (a third above the third).
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.
Augmented triads are composed of a major third but an augmented fifth, or a major third on top of a major third (same as a major triad, except the top note has been raised by a semitone). Diminished triads have a minor third and a diminished fifth, or a minor third on a minor third (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:
Types of triads
As well as major and minor, there can also be augmented and diminished triads. These four terms describe the quality of a chord. For instance a triad built on top of a root D in the key of C would be said to be minor or have a minor quality.Chord sequences
Chords are commonly played in sequence, much as notes are played in sequence to form melodies. Chord sequences can be conceptualised either in a simplistic way, in which the root notes of the chords play simple melodies whilst tension is created and relieved by increasing and decreasing dissonance, or full attention can be paid to every note in each chord, in which case chord sequences can be regarded as multi-part harmony of unlimited complexity.
Harmonic Function
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 I, III and VI chord are said to have a Tonic Function, due to the fact that they have a stable sound and do not have a tendency to resolve. When a chord progression resolves to a III or VI chord, it is called a Tonic Substitution, because the stable III or VI chord is being used as a substitute for the expected I chord.
- The VII and the V chord are said to have a Dominant Function, and they have a strong tendency to resolve to other chords. The five down a perfect fifth to the I chord and the VII chord up a minor second to the I chord, due to the expected resolution of the tritone, or the highly unstable diminished fifth which is present in a diatonic VII chord.
- The II and IV chords have Subdominant Function, partially due to the fact that they are a fifth away from the Dominant chords of a key, and partially because in their own Tonic keys, their respective Dominant chords are built on the root notes of the stable Tonic function I and VI. They are also referred to as Dominant Preparation chords, and are used to approach a Dominant function chord. The progression IV-V-I, (subdominant, dominant, tonic) is by far the most common chord progression in all of music, and can be found in an astonishingly wide variety of styles, forms, and genres.
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
viið -- B D F -- dim. -- B dim -- dominantThere 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.
- Root position is when the chord is played in ascending thirds with its root note in the bass.
- First Inversion when the chord consists of a major or minor sixth and a major or minor third, and the third of the chord is in the bass
- Second Inversion when the chord consists of a perfect or, less common, augmented or diminished 4th, and a major or minor sixth, with the fifth of the chord in the bass.
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:Augmented sixth chords
See: Augmented sixth chord.
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.
Borrowed chords
Borrowed chords are chords borrowed from the parallel minor or major. If the root of the borrowed chord is not in the original key, then they are named by the accidental. For instance, in major, a chord borrowed from the parallel minor's sixth degree is a "flat six chord" written bVI. Borrowed chords are an example of mode mixture.
Other types of chords
"Power chords" are simple intervals extended in octaves, rather than true chords, and are used extensively in many kinds of rock music. Polychords are two or more chords superimposed on top of one another.
See also: Tristan chord
Further reading
External links