Sentimental ballads, sometimes called "tear-jerkers" or "drawing-room ballads", had their origins in the early "Tin Pan Alley" music industry of the later 19th century. They were generally sentimental, narrative, strophic songs published separately or as part of an opera, descendants perhaps of broadside ballads.
As new genres of music, such as ragtime, blues and jazz, began to emerge in the early 20th century the popularity of this genre faded, but the association with sentimentality led to the term ballad being used for a slow love song from the 1950s onwards. Today, sentimental ballads are primarily known as pop ballads or power ballads, and they often deal with romantic and sexual relationships.
By the Victorian era, ballad had come to mean any sentimental popular song, especially so-called "royalty ballads". Some of Stephen Foster's songs exemplify this genre. By the 1920s, composers of Tin Pan Alley and Broadway used ballad to signify a slow, sentimental tune or love song, often written in a fairly standardized form. Jazz musicians sometimes broaden the term still further to embrace all slow-tempo pieces.
When the word ballad appears in the title of a song, as for example in The Beatles' "The Ballad of John and Yoko" or Billy Joel's "The Ballad of Billy the Kid", the folk music sense is generally implied. Ballad is also sometimes applied to strophic story-songs more generally, such as Don McLean's "American Pie".
Pop ballads tend to have a lush arrangement, where emphasis on melody and harmonies is emphasized. They are usually melodic enough to get the listener's attention, and may also work well as background music. Ballads tend to be written in a basic format employing a verse–chorus structure. Ballads mostly use acoustic instruments such as acoustic guitars, pianos, saxophones, and sometimes an orchestral set. The electric guitars are normally faint and high-pitched. However, recent ballads may usually feature synthesizers and other electronics, such as drum machines.
Jazz and traditional pop
Most pop standard and jazz ballads are built from a single, introductory verse; usually around 16 bars in length, and ending on the dominant; the chorus or refrain, usually it is 16 or 32 bars long, and in AABA form (though other forms such as ABAC are not uncommon). In AABA forms, the B section is usually referred to as the bridge; often a brief coda, sometimes based on material from the bridge, was added as in "Over the Rainbow".
Other key traditional pop and jazz ballads include: "Body and Soul" by Johnny Green; "Misty" by Erroll Garner; "The Man I Love" by George Gershwin; "My Funny Valentine" by Rodgers and Hart, "God Bless the Child" by Billie Holiday, "Ev'ry Time We Say Goodbye" by Cole Porter, the instrumental ballad "Naima" by John Coltrane, "In a Sentimental Mood" by Duke Ellington and "Always" by Irving Berlin.
Pop and R&B ballads
The most common use of the term ballad in modern pop and R&B music is for an emotional love song. Examples of pop ballads include, Celine Dion's "My Heart Will Go On", Whitney Houston's "I Will Always Love You", Mariah Carey's "We Belong Together" and "Almost Home", Kelly Clarkson's "Because of You", Britney Spears's "Everytime", Toni Braxton's "Un-Break My Heart", Beyonce's "Listen", George Michael's "Careless Whisper", Sinead O'Connor's "Nothing Compares 2 U", Jessica Simpson's "I Wanna Love You Forever" and Tamar Braxton's "If I Don't Have You".
Simon Frith, the British sociomusicologist and former rock critic, identifies the origins of the power ballad in the emotional singing of soul artists, particularly Ray Charles, and the adaptation of this style by performers such as Eric Burdon, Tom Jones, and Joe Cocker to produce slow-tempo songs often building to a loud and emotive chorus backed by drums, electric guitars, and sometimes choirs. According to Charles Aaron, power ballads came into existence in the early 1970s, when rock stars attempted to convey profound messages to audiences.
Aaron argues that the power ballad broke into the mainstream of American consciousness in 1976 as FM radio gave a new lease of life to earlier songs such as Led Zeppelin's "Stairway to Heaven" (1971), Aerosmith's "Dream On" (1973), and Lynyrd Skynyrd's "Free Bird" (1974). The Carpenters' "Goodbye to Love" (1972) has also been identified as a prototype of the power ballad. Notable power ballad examples include Nazareth's version of "Love Hurts" (1975), Foreigner's "I Want to Know What Love Is" (1984), Scorpions' "Still Loving You" (1984), Heart's "What About Love" (1985), Whitesnake's "Is This Love" (1987), and Poison's "Every Rose Has Its Thorn" (1988) 
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