Form in pop/rock music – Formal containers and module structures

Formal Containers


A phrase is a musical unit that typically lasts for four bars and includes one line of poetry for its lyrical content. Phrases are designated by lower-case letters.


In pop/rock music, a module typically spans between 8 and 24 bars and includes 2–4 phrases. (Some auxiliary modules may contain a single phrase.) A module presents a single formal function (such as A, B, C, V, P, etc.) and presents a complete 2-, 3-, or 4-part pattern. Modules typically set a stanza of lyrics.

Module boundaries are usually made apparent by poetic structure (end of a group of rhyming lines—couplet or stanza) or surface features of the song (clear rhythmic, harmonic, and melodic arrival; change in instrumentation or volume; return to beginning of a previously heard module; etc.).

For instance, take the transition from a verse module to a chorus module at 2:42 in U2’s “Pride (In the Name of Love).” The module boundary is delineated by a number of features simultaneously:

  • The text closes out the verse’s quatrain with a (more-or-less) rhyming lyric (“sky”–”pride”) before beginning a new stanza.
  • The end of the verse is signaled by a drum fill, a common end-of-phrase or end-of-module gesture.
  • The general dynamic gets louder very quickly.
  • The guitar becomes more active, and is doubled by a second guitar part.
  • The lead vocals rise in register.
  • Background vocals are added to the lead vocal part.

All of these features help delineate the boundary between modules, and most of them also give the new module (the chorus) a higher eneregy level than the previous module (the verse).

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All module definitions are based on Jason Summach’s (2012) dissertation, “Form in Top-20 Rock Music, 1955–89.”

Primary module

“A module that contains a song’s principal materials” (Summach, p. 322), such as the title text or the most memorable or climactic music. Primary modules exhibit strophe function (A) or chorus function (C). See Formal functions for more details on these specific functions.

Secondary module

A secondary module is a core module that creates a contrast with the primary module or draws attention to it (see Summach, p. 322). Secondary modules exhibit bridge function (B), verse function (V), prechorus function (P), or postchorus function (Z).

Core module

Core modules form the main musical and poetic content of a song. All primary and secondary modules are considered core modules. (See Summach, p. 321.)

Auxiliary module

Auxiliary modules help frame the core modules, introducing them, providing temporary relief from them, or winding down from them. They exhibit introduction function (I), outro function (O), or coda function (X). (See Summach, p. 321.)


“The characteristic succession of modules in a song form, ending with the song’s primary module type” (Summach, p. 321). A cycle contains one or more modules, typically in the same order (though sometimes with one or more modules omitted, especially toward the end of a song). Curly brackets {} are used to refer to cycles (to differentiate them from names of song form types).

A strophic song’s cycle is {A}. Since there is only one module in a strophic cycle, analysis of the cycles is trivial and can be easily passed over.

A 32-bar song’s cycle is typically {AABA}, though abbreviated cycles are common, especially later in the song. “I Want to Hold Your Hand” is a typical example, where a complete {AABA} cycle is followed by an abbreviated {BA} cycle (see Pop/rock form overview for a detailed explanation):


A verse-chorus song’s main cycle is typically {VC} or {VPC}. When a bridge occurs in the song, it often replaces V or VP. Postchoruses (Z) can also follow the chorus.

Bon Jovi’s “Livin’ on a Prayer” (discussed in the Pop/rock form overview) contains a moderately complex set of cycles:


Note the use of a mid-song introduction between cycles, and the use of an instrumental chorus (guitar solo) to begin the third cycle, where we might also expect a bridge. The outro is chorus-based, simply a repetition of the chorus ― an example of chorusification.

Module structures

Two-part (aa’)

A module is two-part when the phrases that make up the module can be grouped into a first half and a second half. In two-part modules, the second half is usually based on the same music as the first half, and thus it is labeled aa’. Often these two halves begin the same but have different endings, participating in an antecedent–consequent (weak → strong) relationship.

The chorus to “Livin’ on a Prayer” has an a a’ structure. The first four-bar phrase (“Oh, we’re half-way there…”) and the second four-bar phrase (“Take my hand…”) have identical melody and harmony (hence the a), but different lyrics (hence the prime). Note that in many songs, this relationship is not as clear cut. However, if the two phrases begin with similar musical material, give them the same letter. New lyrics, new musical endings, or musical variations simply warrant a “prime.”

Two-part – ab

Very rarely a module’s phrases can be grouped into two clear halves based on different music. Such a module is labeled ab.

Three-part – aa’b

A module containing three phrases is a three-part module. If the first two phrases are based on the same music, the module is labeled aa’b.

12-bar blues progressions are the most common example of a three-part aa’b module. “Hound Dog” (on the blues-progression page) contains aa’b strophes.

Three-part – abb’

If the second and third phrases in a three-part module are based on the same music, the module is labeled abb’.

Four-part – srdc

A module composed of four phrases often contains a sentential structure (presentation → continuation → cadential/conclusion). In pop/rock music, this often appears as a basic musical idea in the first phrase, a repetition or “response” to it in the second, contrasting material in the third phrase (often employing fragmentation, acceleration of harmonic rhythm, and movement away from tonic harmony), and a conclusion in the fourth phrase ― either with a return to the basic idea and tonic harmony or with still newer material that forms a strong melodic, rhythmic, and harmonic conclusion. Walter Everett has called such a four-phrase sentential structure in pop/rock music srdc (statement, restatement/response, departure, conclusion).

In conventional lettering, an srdc module could employ an aaba structure (with statement material returning as a restatement and again as the conclusion), or aabc structure (where the conclusion material is new). Occasionally abcd or abca are possible, but only if b is a clear response to a, not simply new material.

srdc structures tend to divide neatly into halves: sr and dc.

Carl Perkins’s “Blue Suede Shoes” contains a clear srdc structure in its second strophe (0:19; find a recording and complete module analysis on the Pop/rock form overview). It contains four four-bar phrases (following a 16-bar blues structure). The first two phrases (statement–restatement) contain the same harmony (tonic prolongation), melodies which begin identically, and though the lyrics differ, the rhythmic and rhyme schemes are the same. The third phrase (departure) brings a new melody, new harmony (move to the subdominant), and the title lyrics (this is a refrain shared with other strophes in the song). The final phrase (conclusion) closes out the poetic unit and the blues harmonic progression.

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