Thirty-two-bar form
The thirty-two-bar form, also known as the AABA song form, American popular song form and the ballad form, is a song structure commonly found in Tin Pan Alley songs and other American popular music, especially in the first half of the 20th century.
Examples of 32-bar AABA form songs include:
"Over the Rainbow", "What’ll I Do", "Make You Feel My Love", and "Blue Skies". Other examples include Willie Nelson's "Crazy".
At its core, the basic AABA 32-bar song form consists of four sections, each section being 8 bars in length, totaling 32 bars. Each of these 8-bar sections is assigned a letter name ("A" or "B"), based on its melodic and harmonic content. The A sections all share the same melody (possibly with slight variations), and the recurring title lyric typically falls on either the first or last line of each A section. The "B" section musically and lyrically contrasts the A sections, and may or may not contain the title lyric. The "B" section may use a different harmony that contrasts with the harmony of the A sections. For example in the song "I've Got Rhythm", the A sections are in the key of B♭, but the B section involves a circle of fifths series of dominant seventh chords going from D7, G7, C7 to F7. Song form terminology is not standardized, and the B section is also referred to as the "middle eight", "bridge", or "primary bridge".
The song form of "What'll I Do" by Irving Berlin is as follows:
Some Tin Pan Alley songs composed as numbers for musicals precede the main tune with what was called a "sectional verse" or "introductory verse" in the terminology of the early 20th century. This introductory section is usually sixteen bars long and establishes the background and mood of the number, and is musically undistinguished in order to highlight the attractions of the main tune. The sectional verse is often omitted from modern performances. It is not assigned a letter in the "AABA" naming scheme.
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