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Chord (music)In music and music theory, a chord (from the middle English cord, short for accord) is three or more different notes or pitches sounding simultaneously, or nearly simultaneously, over a period of time. For example, if you simultaneously play any three (or more) keys of a piano, you have just played a chord. Likewise, if you simultaneously play three or more strings of a guitar, you have just played a chord on the guitar. Every chord is given a specific name, based on the notes that constitute the chord and the distances, or intervals, between them.Originally, a chord simply meant the sounding together of different tones, the resultant of these tones. 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. Chords being directly perceived units, sonorities of two pitches are often interpreted as fragments of three- or four-note chords. 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. Although, as Jean-Jacques Nattiez (1990, p.218) explains, "we can encounter 'pure chords' in a musical work," such as in the following example from the "Promenade" of Modest Mussorgsky's Pictures at an Exhibition:
But "often, we must go from a textual given to a more abstract representation of the chords being used," as in the following example where the chords on the second stave are abstracted from the actual notes written on the first:
"For a sound configuration to be recognized as a chord, it must have a certain duration." Goldman (1965, p.26) elaborates: "the sense of harmonic relation, change, or effect depends on speed (or tempo) as well as on the relative duration of single notes or triadic units. Both absolute time (measurable length and speed) and relative time (proportion and division) must at all times be taken into account in harmonic thinking or analysis." Music is said to be chord-based when the melody is determined by the chords and not by melodic concerns such as modal frames. Nonchord tones and dissonanceA 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.Chord sequencesChords 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 while tension is created and relieved by increasing and decreasing dissonance, or full attention can be paid to each note in every chord, in which case chord sequences can be regarded as multi-part harmony of unlimited complexity.Listen to an example of a chord sequence from Erik Satie's Sarabande no. 3. Harmonic analysis and constructionChords are named for how many notes they contain, more commonly for what type of intervals they are constructed from, and by the root note and bass note.The easiest way to name a chord, or limit its construction, is according to the number of notes included. The simplest and possibly most frequently used chords are trichords, meaning they have three ("tri") notes (before any doubling of notes, that is), 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 chords most traditionally used in Western music are those with notes fundamentally a third apart (that is, before any inversions and doublings, discussed below), called tertian chords. Chords constructed from seconds are secundal, and from fourths are quartal. Chords are also distinguished and notated by the scale degree, pitch, or note of their root and bass, although there are many different conventions for indicating the quality of the chord, and the inversion of the chord (determined by which note of the chord serves as the bass note); see Inverted Triads below). 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 fulfilling, and that any special role of the chord outside of its normal diatonic function would be inferred from the context. Chords are labelled with chord symbols. The triadThe most commonly used chords in Western music, triads 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 a third above that note, and therefore a fifth above the root.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 the root) 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 triad, F is always the root, A (sharp, natural, or flat) is always the third, and C (sharp, natural, or flat) is always the fifth. For another example, consider an octave of the C major scale, consisting 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 (while the outer notes are still a perfect fifth apart). This triad on C is therefore called a major triad, or major chord, since the interval from C to E is 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 before returning to a C, in this case), which is diminished. See also Mathematics of the Western music scale. Types of triadsAs 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.Augmented triads are composed of the root, a note a major third from the root, but then a note an augmented fifth from the root (unlike the major and minor triads); or equivalently, 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 the root, a note a minor third from the root, but then a note a diminished fifth from the root, 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:
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