Guitar chord

In music, a guitar chord is a set of notes played on a guitar. A chord's notes are often played simultaneously, but they can be played sequentially in an arpeggio. The implementation of guitar chords depends on the guitar tuning. Most guitars used in popular music have six strings with the "standard" tuning of the Spanish classical guitar, namely E–A–D–G–B–E' ; in standard tuning, the intervals present among adjacent strings are perfect fourths except for the major third. Standard tuning requires four chord-shapes for the major triads.
There are separate chord-forms for chords having their root note on the third, fourth, fifth, and sixth strings. For a six-string guitar in standard tuning, it may be necessary to drop or omit one or more tones from the chord; this is typically the root or fifth. The layout of notes on the fretboard in standard tuning often forces guitarists to permute the tonal order of notes in a chord.
The playing of conventional chords is simplified by open tunings, which are especially popular in folk, blues guitar and non-Spanish classical guitar. For example, the typical twelve-bar blues uses only three chords, each of which can be played by fretting six strings with one finger. Open tunings are used especially for steel guitar and slide guitar. Open tunings allow one-finger chords to be played with greater consonance than do other tunings, which use equal temperament, at the cost of increasing the dissonance in other chords.
The playing of guitar chords is simplified by the class of alternative tunings called regular tunings, in which the musical intervals are the same for each pair of consecutive strings. Regular tunings include major-thirds tuning, all-fourths, and all-fifths tunings. For each regular tuning, chord patterns may be diagonally shifted down the fretboard, a property that simplifies beginners' learning of chords and that simplifies advanced players' improvisation. On the other hand, in regular tunings 6-string chords are more difficult to play.
Conventionally, guitarists double notes in a chord to increase its volume, an important technique for players without amplification; doubling notes and changing the order of notes also changes the timbre of chords. It can make possible a "chord" which is composed of the all same note on different strings. Many chords can be played with the same notes in more than one place on the fretboard.

Musical fundamentals

The theory of guitar-chords respects harmonic conventions of Western music. Discussions of basic guitar-chords rely on fundamental concepts in music theory: the twelve notes of the octave, musical intervals, chords, and chord progressions.

Intervals

The octave consists of twelve notes.
Its natural notes constitute the C major scale,.
The intervals between the notes of a chromatic scale are listed in a table, in which only the emboldened intervals are discussed in this article's section on fundamental chords; those intervals and other seventh-intervals are discussed in the section on intermediate chords. The unison and octave intervals have perfect consonance. Octave intervals were popularized by the jazz playing of Wes Montgomery. The perfect-fifth interval is highly consonant, which means that the successive playing of the two notes from the perfect fifth sounds harmonious.
A semitone is the distance between two adjacent notes on the chromatic circle, which displays the twelve notes of an octave.

Number of semitones	Minor, major, or perfect intervals	Audio	Harmoniousness
0	Perfect unison		Open consonance
1	Minor second		Sharp dissonance
2	Major second		Mild dissonance
3	Minor third		Soft consonance
4	Major third		Soft consonance
5	Perfect fourth		Ambivalence
6	Augmented fourth		Ambiguous
7	Perfect fifth		Open consonance
8	Minor sixth		Soft consonance
9	Major sixth		Soft consonance
10	Minor seventh		Mild dissonance
11	Major seventh		Sharp dissonance
12	Octave		Open consonance

As indicated by their having been emboldened in the table, a handful of intervals—thirds, perfect fifths, and minor sevenths—are used in the following discussion of fundamental guitar-chords.
As already stated, the perfect-fifths interval is the most harmonious, after the unison and octave intervals. An explanation of human perception of harmony relates the mechanics of a vibrating string to the musical acoustics of sound waves using the harmonic analysis of Fourier series. When a string is struck with a finger or pick, it vibrates according to its harmonic series. When an open-note C-string is struck, its harmonic series begins with the terms. The root note is associated with a sequence of intervals, beginning with the unison interval, the octave interval, the perfect fifth, the perfect fourth, and the major third. In particular, this sequence of intervals contains the thirds of the C-major chord.

Perfect fifths

The perfect-fifth interval is featured in guitar playing and in sequences of chords. The sequence of fifth intervals built on the C-major scale is used in the construction of triads, which is discussed below.

Cycle of fifths

Concatenating the perfect fifths ,,,,, yields the sequence of fifths ; this sequence of fifths displays all the notes of the octave. This sequence of fifths shall be used in the discussions of chord progressions, below.

Power chord

The perfect-fifth interval is called a power chord by guitarists, who play them especially in blues and rock music. The Who's guitarist, Peter Townshend, performed power chords with a theatrical windmill-strum. Power chords are often played with the notes repeated in higher octaves.
Although established, the term "power chord" is inconsistent with the usual definition of a chord in musical theory, which requires three distinct notes in each chord.

Chords in music theory

;A brief overview
The musical theory of chords is reviewed, to provide terminology for a discussion of guitar chords. Three kinds of chords, which are emphasized in introductions to guitar-playing, are discussed. These basic chords arise in chord-triples that are conventional in Western music, triples that are called three-chord progressions. After each type of chord is introduced, its role in three-chord progressions is noted.
Intermediate discussions of chords derive both chords and their progressions simultaneously from the harmonization of scales. The basic guitar-chords can be constructed by "stacking thirds", that is, by concatenating two or three third-intervals, where all of the lowest notes come from the scale.

Triads

Major

Both major and minor chords are examples of musical triads, which contain three distinct notes. Triads are often introduced as an ordered triplet:

the root;
the third, which is above the root by either a major third or a minor third ;
the fifth, which is a perfect fifth above the root; consequently, the fifth is a third above the third—either a minor third above a major third or a major third above a minor third. The major triad has a root, a major third, and a fifth.

Chord	Root	Major third	Fifth
C	C	E	G
D	D	F	A
E	E	G	B
F	F	A	C
G	G	B	D
A	A	C	E
B	B	D	F

For example, a C-major triad consists of the -notes.
The three notes of a major triad have been introduced as an ordered triplet, namely, where the major third is four semitones above the root and where the perfect fifth is seven semitones above the root. This type of triad is in closed position. Triads are quite commonly played in open position: For example, the C-major triad is often played with the third and fifth an octave higher, respectively sixteen and nineteen semitones above the root. Another variation of the major triad changes the order of the notes: For example, the C-major triad is often played as, where is a perfect fifth and E is raised an octave above the perfect third. Alternative orderings of the notes in a triad are discussed below.
In popular music, a subset of triads is emphasized—those with notes from the three major-keys, which also contain the notes of their relative minor keys.

Progressions

The major chords are highlighted by the three-chord theory of chord progressions, which describes the three-chord song that is archetypal in popular music. When played sequentially, the chords from a three-chord progression sound harmonious.
The most basic three-chord progressions of Western harmony have only major chords. In each key, three chords are designated with the Roman numerals : The tonic, the subdominant, and the dominant. While the chords of each three-chord progression are numbered, they appear in other orders.

Key	Tonic	Subdominant	Dominant
C	C	F	G
D	D	G	A
E	E	A	B
G	G	C	D
A	A	D	E

In the 1950s the I–IV–V chord progression was used in "Hound Dog" and in "Chantilly Lace".
Major-chord progressions are constructed in the harmonization of major scales in triads. For example, stacking the C-major scale with thirds creates a chord progression, which is traditionally enumerated with the Roman numerals I, ii, iii, IV, V, vi, vii; its sub-progression C–F–G is used in popular music, as already discussed. Further chords are constructed by stacking additional thirds. Stacking the dominant major-triad with a minor third creates the dominant seventh chord, which shall be discussed after minor chords.