Such composers as Rodgers and Hart (in their 1934 song "Blue Moon"), and Hoagy Carmichael and Frank Loesser (in their 1938 "Heart and Soul") used a I–vi–ii–V-loop chord progression in those hit songs; composers of doo-wop songs varied this slightly but significantly to the chord progression I–vi–IV–V, so influential that it is sometimes referred to as the '50s progression. This characteristic harmonic layout was combined with the AABA chorus form typical for Tin Pan Alley songs.Ralf von Appen, Markus Frei-Hauenschild (2015). "AABA, Refrain, Chorus, Bridge, Prechorus — Song Forms and their Historical Development". In: Samples. Online Publikationen der Gesellschaft für Popularmusikforschung/German Society for Popular Music Studies e.V., Ed. by Ralf von Appen, André Doehring and Thomas Phleps. Vol. 13, p. 6.
Such composers as Rodgers and Hart (in their 1934 song "Blue Moon"), and Hoagy Carmichael and Frank Loesser (in their 1938 "Heart and Soul") used a I–vi–ii–V-loop chord progression in those hit songs; composers of doo-wop songs varied this slightly but significantly. to the chord progression I–vi–IV–V, so influential that it is sometimes referred to as the '50s progression. This characteristic harmonic layout was combined with the AABA chorus form typical for Tin Pan Alley songs.Ralf von Appen, Markus Frei-Hauenschild (2015). "AABA, Refrain, Chorus, Bridge, Prechorus — Song Forms and their Historical Development". In: Samples. Online Publikationen der Gesellschaft für Popularmusikforschung/German Society for Popular Music Studies e.V., Ed. by Ralf von Appen, André Doehring and Thomas Phleps. Vol. 13, p. 6