Strophic form
Strophic form, or chorus form, is a sectional and/or additive way of structuring a piece of music based on the repetition of one formal section or block played repeatedly. It is the musical analogue of repeated stanzas in poetry or lyrics: where the text repeats the same rhyme scheme from one stanza to the next, the accompanying music for each stanza is either the same or very similar from one stanza to the next.
It may be considered AAA... or AA'A"....
Most folk and popular songs are strophic in form, including the twelve bar blues. Thus the "verse-chorus-verse" of most popular music songs is a strophic verse-refrain form. The chorus often sharply constrasts the verse melodically, rhythmically, and harmonically, and assumes a higher level of dynamics and activity, often with added instrumentation. In addition, many songs from the classical music tradition are in strophic form, from the 14th century French rondeau of the ars nova, to the 17th century French air de cour, to the 19th century German lieder; indeed strophic form has been one of the must durable of all musical forms, probably because it is intuitively most obvious to have similar music accompanying repeated stanzas of verse.
A very similar form is theme and variations form. In this form, there is a musical melody (the theme), followed by many altered versions of it (the variations). The variations are all altered forms of the theme; the theme is always present, in some form however disguised, in each of the variations. The theme may be either original or previously written by another composer.
