At the beginning of our discussion of jazz we stressed that it is not a genre of music, but a performance style that went through many developments. As we trace these developments — from New Orleans jazz to swing, bebop, and the rest — we should pause for a moment to consider the material for jazz in its various styles. Blues are iconic, but blues underpin only a small minority of jazz performances. Mostly jazz musicians work their magic on popular songs, and American popular song of the twentieth century is a major vernacular repertory, in a way as important as jazz itself. It flourished in the first half of the century at the hands of a cadre of composers who are household names: Irving Berlin (1888–1989), Jerome Kern (1885–1945), Cole Porter (1891–1964), George Gershwin (1898–1937), and many others.

Early jazz is associated with New Orleans because the players came from there. Popular song is associated with Tin Pan Alley, a district in New York (which relocated a couple of times) where music publishers had their shops and offices. The songs they bought for a pittance they sold as sheet music in as many as a million copies, sometimes, meanwhile collecting royalties on radio and stage performances. It’s been said that popular songs are the songs you forgot you knew but remember when you hear the chorus, songs sung in kindergarten as well as in the retirement home: “Blue Skies,” “White Christmas,” and “God Bless America” (Berlin); “Smoke Gets In Your Eyes” and “The Way You Look Tonight” (Kern); “Lady Be Good,” “Somebody Loves Me,” and “The Man I Love” (Gershwin) — we could go on and on.

Tin Pan Alley songs were usually simple in construction, easy to hum: a chorus, typically in a form such as a a b a or a b a b, and a couple of verses — which tend to be forgotten; it’s just the chorus that, once you recall it, you can’t get out of your head. Not only were jazz and popular song simultaneous developments, one can see that they fed on each other. Jazz musicians needed material for their improvisations and arrangements. Popular songs needed the artistry and expansion of jazz to become impressive listening experiences.

Songs that were favored by jazzmen were called “standards.” To become a standard, however, such songs needed to catch on with the public through versions by the best-loved singers of the day. Vocalists like Bing Crosby and Frank Sinatra sang the sentimental, jazzy tunes to dance-hall audiences, to the ever-growing radio audience, in the movies, and — most important by the end of the 1940s — on records.