Chord progression

In these genres, chord progressions are the defining feature on which melody and rhythm are built.

In rock and blues, musicians also often refer to chord progressions using Roman numerals, as this facilitates transposing a song to a new key.

In addition, the seventh degree of the major scale (i.e. the leading tone) forms a diminished chord (viio).

This in turn may lead to a resolution back to the original key later on, so that the entire sequence of chords helps create an extended musical form and a sense of movement.

[citation needed] In western classical notation, chords are numbered with Roman numerals.

In considering Arab and Indian music, where diatonic scales are used, there are also available a number of non-diatonic scales, the music has no chord changes, remaining always upon the key-chord, an attribute which has also been observed in hard rock, hip hop,[5] funk, disco,[6] jazz, etc.

[2] For example, many of the more straightforward melodies in classical music consist entirely or mostly of alternation between the tonic (I) and the dominant (V, sometimes with an added seventh), as do popular songs such as "Achy Breaky Heart".

Where such a simple sequence does not represent the entire harmonic structure of a piece, it may readily be extended for greater variety.

The 12-bar blues and its many variants use an elongated, three-line form of the I–IV–V progression that has also generated countless hit records, including the most significant output of rock and rollers such as Chuck Berry and Little Richard.

This progression had been in use from the earliest days of classical music and then generated popular hits such as Rodgers and Hart's "Blue Moon" (1934)[11] and Hoagy Carmichael's "Heart and Soul" (1938).

[12] Taken up into the pop mainstream, it continued to be used sectionally, as in the last part of The Beatles' "Happiness Is a Warm Gun".

[15] Short cyclical progressions may be derived by selecting a sequence of chords from the series completing a circle from the tonic through all seven diatonic chords:[15]I–IV–viio–iii–vi–ii–V–IThis type of progression was much used by classical composers, who introduced increasingly subtle inflections.

Particularly, substitution of major for minor chords giving, for example, I–VI–II–V allowed a more sophisticated chromaticism as well as the possibility of modulation.

The finale measures of the first movement of Ravel's Piano Concerto in G feature the harmonization of a descending hybrid scale (phrygo-major).

A notable example of a descending minor chord progression is the four-chord Andalusian cadence, i–VII–VI–V.

Folk and blues tunes frequently use the Mixolydian scale, which has a flat seventh degree, altering the position of the three major chords to I–♭VII–IV.

According to Tom Sutcliffe:[17] ... during 1960s some pop groups started to experiment with modal chord progressions as an alternative way of harmonizing blues melodies.

This phenomenon is also linked to the rise in use of power chords in various sub-genres of rock music.

The key note, or tonic , of a piece of music is called note number one, the first step of (here), the ascending scale iii–IV–V. Chords built on several scale degrees are numbered likewise. Thus the chord progression E minor–F–G can be described as three–four–five, (or iii–IV–V).