In amusical composition, achord progression orharmonic progression (informallychord changes, used as aplural) is a succession ofchords. Chord progressions are the foundation ofharmony in Western musical tradition from thecommon practice era ofClassical music to the 21st century. Chord progressions are the foundation ofpopular music styles (e.g.,pop music,rock music),traditional music, as well as genres such asblues andjazz. In these genres, chord progressions are the defining feature on whichmelody andrhythm are built.

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A IV–V–I progression in the key of C major. The chords shown are F major, G major, and C major.

In tonal music, chord progressions have the function of either establishing or otherwise contradicting atonality, the technical name for what is commonly understood as the "key" of a song or piece. Chord progressions, such as the extremely common chord progression I-V-vi-IV, are usually expressed byRoman numerals in Classical music theory. In many styles of popular and traditional music, chord progressions are expressed using the name and "quality" of the chords. For example, the previously mentioned chord progression, in the key of E♭ major, would be written as E♭ major–B♭ major–C minor–A♭ major in a fake book orlead sheet. In the first chord, E♭ major, the "E♭" indicates that the chord is built on theroot note "E♭" and the word "major" indicates that amajor chord is built on this "E♭" note.

In rock and blues, musicians also often refer to chord progressions usingRoman numerals, as this facilitates transposing a song to a new key. For example, rock and blues musicians often think of the12-bar blues as consisting of I, IV, and V chords. Thus, a simple version of the 12-bar blues might be expressed as I–I–I–I, IV–IV–I–I, V–IV–I–I. By thinking of this blues progression in Roman numerals, abackup band orrhythm section could be instructed by abandleader to play the chord progression in any key. For example, if the bandleader asked the band to play this chord progression in the key of B♭ major, the chords would be B♭-B♭-B♭-B♭, E♭-E♭-B♭-B♭, F-E♭-B♭-B♭.

The complexity of a chord progression varies from genre to genre and over different historical periods. Some pop and rock songs from the 1980s to the 2010s have fairly simple chord progressions.Funk emphasizes thegroove and rhythm as the key element, so entire funk songs may be based on one chord. Somejazz-funk songs are based on a two-, three-, or four-chordvamp. Somepunk andhardcore punk songs use only a few chords. On the other hand,bebop jazz songs may have32-bar song forms with one or two chord changes every bar.

A chord may be built upon any note of amusical scale. Therefore, a seven-notediatonic scale allows seven basicdiatonic triads, each degree of the scale becoming theroot of its own chord.^[1] A chord built upon the note E is an E chord of sometype (major, minor, diminished, etc.) Chords in a progression may also have more than three notes, such as in the case of aseventh chord (V⁷ is particularly common, as it resolves to I) or anextended chord. The harmonicfunction of any particular chord depends on the context of the particular chord progression in which it is found.^[2]

The diatonic harmonization of anymajor scale results in threemajor triads, which are based on the first, fourth, and fifthscale degrees. The triads are referred to as thetonic chord (inRoman numeral analysis, symbolized by "I"), thesubdominant chord (IV), and thedominant chord, (V), respectively.^[3] These three triads include, and therefore canharmonize, every note of that scale. Many simpletraditional music,folk music androck and roll songs use only these three chord types (e.g.The Troggs' "Wild Thing", which uses I, IV and V chords).

The same major scale also has threeminor chords, thesupertonic chord (ii),mediant chord (iii), andsubmediant chord (vi), respectively. These chords stand in the same relationship to one another (in therelative minor key) as do the three major chords, so that they may be viewed as the first (i), fourth (iv) and fifth (v) degrees of the relative minor key. For example, the relative minor of C major is A minor, and in the key of A minor, the i, iv and v chords are A minor, D minor and E minor. In practice, in a minor key, thethird of the dominant chord is often raised by one semitone to form a major chord (or adominant seventh chord if theseventh is added).

In addition, the seventh degree of the major scale (i.e. theleading tone) forms adiminished chord (vii^o).^[4]

A chord may also havechromatic notes, that is, notes outside of the diatonic scale. Perhaps the most basic chromaticalteration in simple folk songs is the raised fourth degree (♯ ) that results when thethird of the ii chord is raised onesemitone. Such a chord typically functions as thesecondary dominant of the V chord (V/V). In some instances, chromatic notes are introduced tomodulate to a new key. This in turn may lead to aresolution back to the original key later on, so that the entire sequence of chords helps create an extendedmusical form and a sense of movement.

Although there are many possible progressions, in practice, progressions are often limited to a few bars' lengths and certain progressions are favored above others. There is also a certain amount of fashion in which a chord progression is defined (e.g., the12-bar blues progression) and may even help in defining an entiregenre.^{[citation needed]}

In westernclassical notation, chords are numbered with Roman numerals. Other types ofchord notation have been devised, fromfigured bass to thechord chart. These usually allow or even require a certain amount ofimprovisation.

Diatonic scales such as themajor and minor scales lend themselves particularly well to the construction of common chords because they contain manyperfect fifths. Such scales predominate in those regions where harmony is an essential part of music, as, for example, in thecommon practice period of western classical music. In consideringArab andIndian 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 inhard rock,hip hop,^[5]funk,disco,^[6]jazz, etc.

Alternation between two chords may be thought of as the most basic chord progression. Many well-known pieces are built harmonically upon the mere repetition of two chords of the same scale.^[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 anadded seventh), as do popular songs such as "Achy Breaky Heart".^[7]The Isley Brothers' "Shout" uses I–vi throughout.^[8]

Three-chord progressions are more common since a melody may then dwell on any note of the scale. They are often presented as successions of four chords (as shown below), in order to produce a binaryharmonic rhythm, but then two of the four chords are the same.

• I – IV – V – V
• I – I – IV – V
• I – IV – I – V
• I – IV – V – IV

Often the chords may be selected tofit a pre-conceived melody, but just as often it is the progression itself that gives rise to the melody.

Similar progressions abound inAfrican popular music. They may be varied by the addition ofsevenths (or otherscale degrees) to any chord or by substitution of therelative minor of the IV chord to give, for example, I–ii–V. This sequence, using theii chord, is also usedcadentially in a common chord progression ofjazz harmony, the so-calledii–V–I turnaround.

Three-chord progressions provide the harmonic foundation of much African and American popular music, and they occur sectionally in many pieces of classical music (such as the opening bars ofBeethoven'sPastoral Symphony^[9]).

Where such a simple sequence does not represent the entire harmonic structure of a piece, it may readily be extended for greater variety. Frequently, an openingphrase has the progression I–IV–V–V, which ends on anunresolveddominant, may be "answered" by a similar phrase that resolves back onto thetonic chord, giving a structure of double the length:

I	IV	V	V
I	IV	V	I

Additionally, such a passage may be alternated with a different progression to give a simplebinary orternary form such as that of the popular32-bar form (seemusical form).

The12-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 ofrock and rollers such asChuck Berry andLittle Richard. In its most elementary form (and there are many variants), the chord progression is

I	I	I	I
IV	IV	I	I
V	IV	I	I

Blues progressions have also been subjected to densely chromatic elaboration, as in theBird blues.

Steedman (1984) proposed that a set of recursiverewrite rules generate allwell-formedtransformations of jazz, both basic blues chord changes and slightly modified sequences (such as the "rhythm changes"). Important transformations include:

• replacement of (or addition to) a chord with its dominant, subdominant or thetritone substitution.
• use of chromatic passing chords.
• extensively applying theii–V–I turnaround.
• chord alterations such as minor chords, diminished sevenths, etc.^[10]

Another common way of extending the I–IV–V progression is by adding the chord of the sixth scale degree, giving the sequence I–vi–IV–V orI–vi–ii–V, sometimes called the50s progression or doo-wop progression.

This progression had been in use from the earliest days of classical music and then generated popular hits such asRodgers and Hart's "Blue Moon" (1934)^[11] andHoagy 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".^[13]

Introducing the ii chord into these progressions emphasises their appeal as constituting elementary forms ofcircle progression. These, named for thecircle of fifths, consist of "adjacentroots in ascending fourth or descending fifth relationship"—for instance, the sequence vi–ii–V–I ascends with each successive chord to one a fourth above the previous. Such a motion, based upon close harmonic relations, offers "undoubtedly the most common and the strongest of all harmonic progressions".^[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–vii^o–iii–vi–ii–V–I

This 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 sophisticatedchromaticism as well as the possibility ofmodulation. These harmonic conventions were taken up by American popular entertainers, giving rise to many variations on those harmonic staples of earlyjazz that have been dubbed theragtime progression and thestomp progression. All such progressions may be found used sectionally, as for example in the much-used "rhythm changes" ofGeorge Gershwin's "I Got Rhythm".

As well as the cyclical underpinning of chords, the ear tends to respond well to a linear thread; chords following the scale upwards or downwards. These are often referred to as step progressions^[16] because they follow the steps of the scale, making the scale itself abassline. In the 17th century, descending bass lines found favour for"divisions on the ground", so thatPachelbel's canon contains very similar harmonizations of the descending major scale.

At its simplest, this descending sequence may simply introduce an extra chord, either III or V, into the I–vi–IV–V type of sequence described above. This chord allows the harmonization of theseventh degree, and so of the bass line I–VII–VI....

The finale measures of the first movement ofRavel'sPiano Concerto in G feature the harmonization of a descending hybrid scale (phrygo-major). In this special case, Ravel used a parallel series of major triads (G F♯ E D C B♭ A♭ G).

Similar strategies to all the above, work equally well inminor modes: there have been one-, two-, and three-minor-chord songs,minor blues. A notable example of a descending minor chord progression is the four-chordAndalusian cadence, i–VII–VI–V.

Folk and blues tunes frequently use theMixolydian scale, which has a flat seventh degree, altering the position of the three major chords to I–^♭VII–IV. For example, if the major scale of C, which gives the three chords C, F and G on the first, fourth and fifth degrees, is played with G as the tonic, then the same chords will now appear on the first, fourth, and seventh degrees. A common chord progression with these chords is I-♭VII–IV-I, which also can be played as I-I-♭VII–IV or♭VII–IV-I-I.

The minor-third step from a minor key up to therelative major encouraged ascending scale progressions, particularly based on an ascendingpentatonic scale. Typical of the type is the sequence i–III–IV (or iv)–VI.

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 created a new system of harmony that has influenced subsequent popular music.

This came about partly from the similarity of theblues scale tomodal scales and partly from the characteristics of the guitar and the use of parallel major chords on thepentatonic minor scale. Withbarre chords on guitar, the same chord shape can be moved up and down the neck without changing the fingering. This phenomenon is also linked to the rise in use ofpower chords in various sub-genres ofrock music.

• Chromatic mediant
• Diatonic function
• Ear training
• List of chord progressions
• List of songs containing the 50s progression
• List of songs containing the I–V–vi–IV progression
• Montgomery-Ward bridge
• Passamezzo moderno
• Passing chord
• Root progressions
• Sequence (music)
• Twelve-bar blues
• Traditional sub-Saharan African harmony

• Lloyd, Peter (2014).The Secret Life of Chords: A guide to chord progressions and composition. Australian eBook Publisher.ISBN 9781925029765.
• Middleton, Richard (1990/2002). "Studying Popular Music". Philadelphia: Open University Press.ISBN 0-335-15275-9.
• Nettles, Barrie & Graf, Richard (1997).The Chord Scale Theory and Jazz Harmony. Advance Music,ISBN 3-89221-056-X.
• R., Ken (2012).DOG EAR Tritone Substitution for Jazz Guitar, Amazon Digital Services, Inc., ASIN: B008FRWNIW