Musical form

• a generic type of composition such as the symphony or concerto
• the structure of a particular piece, how its parts are put together to make the whole; this too can be generic, such as binary form or sonata form

There is some overlap between musical form and musical genre. The latter term is more likely to be used when referring to particular styles of music (such as classical music or rock music) as determined by things such as harmonic language, typical rhythms, types of musical instrument used and geographical origin. The phrase musical form is typically used when talking about a particular type or structure within those genres. For example, the twelve bar blues is a specific form often found in the genres of blues and rock and roll music.

Forms and formal detail may be described as sectional or developmental, developmental or variational, syntactical or processual (Keil 1966), embodied or engendered, extensional or intensional (Chester 1970), and associational or hierarchical (Lerdahl 1983). Form may also be described according to symmetries or lack thereof and repetition. A common idea is formal "depth", necessary for complexity, in which foregrounded "detail" events occur against a more structural background. For example: Schenkerian analysis. Fred Lerdahl (1992), among others, claims that popular music lacks the structural complexity for multiple structural layers, and thus much depth. However, Lerdahl's theories explicitly exclude "associational" details which are used to help articulate form in popular music. Allen Forte's book The American Popular Ballad of the Golden Era 1924-1950 analyses popular music with traditional Schenkerian techniques, but this is only possible because pre-rock popular ballads are the genre most accessible similar to the Romantic music that those theories were designed to analyse. (Middleton 1999, p.144)

Extensional music is, "produced by starting with small components - rhythmic or melodic motifs, perhaps - and then 'developing' these through techniques of modification and combination." Intensional music "starts with a framework - a chord sequence, a melodic outline, a rhythmic pattern - and then extends itself by repeating the framework with perpetually varied inflections to the details filling it in." (Middleton, p.142)

Western classical music is the apodigm of the extensional form of musical construction. Theme and variations, counterpoint, tonality (as used in classical composition) are all devices that build diachronically and synchronically outwards from basic musical atoms. The complex is created by combination of the simple, which remains discrete and unchanged in the complex unity...If those critics who maintain the greater complexity of classical music specified that they had in mind this extensional development, they would be quite correct...Rock however follows, like many non-European musics, the path of intensional development. In this mode of construction the basic musical units (played/sung notes) are not combined through space and time as simple elements into complex structures. The simple entity is that constituted by the parameters of melody, harmony, and beat, while the complex is built up by modulation of the basic notes, and by inflexion of the basic beat. All existing genres and sub-types of the Afro-American tradition show various forms of combined intensional and extensional development (Chester 1970, p.78-9).

Middleton (p.145) also describes form, presumably after Gilles Deleuze’s Difference and Repetition (1968, translated 1994), through repetition and difference. Difference is the distance moved from a repeat and a repeat being the smallest difference. Difference is qualitative and quantitative, how far different and what type of difference.

In classical and popular music, there are many labels applied to forms, abstract formal designs, as contrasted with the principals and procedures of combining materials: form. Typical structures used to shape a single movement include:

In a sectional form, the larger unit (form) is built from various smaller clear-cut units (sections) in combination, sort of like stacking legos (DeLone, 1975):