Blues is the name given to both a musical form and a music genre that originated in African-American communities of primarily the "Deep South" of the United States at the end of the 19th century from spirituals, work songs, field hollers, shouts and chants, and rhymed simple narrative ballads. The blues form, ubiquitous in jazz, rhythm and blues, and rock and roll is characterized by specific chord progressions, of which the twelve-bar blues chord progression is the most common. The blue notes that, for expressive purposes are sung or played flattened or gradually bent (minor 3rd to major 3rd) in relation to the pitch of the major scale, are also an important part of the sound.
The blues genre is based on the blues form but possesses other characteristics such as specific lyrics, bass lines and instruments. Blues can be subdivided into several subgenres ranging from country to urban blues that were more or less popular during different periods of the 20th century. Best known are the Delta, Piedmont, Jump and Chicago blues styles. World War II marked the transition from acoustic to electric blues and the progressive opening of blues music to a wider audience, especially white listeners. In the 1960s and 1970s, a hybrid form called blues-rock evolved.
The term "the blues" refers to the "blue devils", meaning melancholy and sadness; an early use of the term in this sense is found in George Colman's one-act farce Blue Devils (1798). Though the use of the phrase in African-American music may be older, it has been attested to since 1912, when Hart Wand's "Dallas Blues" became the first copyrighted blues composition. In lyrics the phrase is often used to describe a depressed mood. The blues form is a cyclic musical form which repeating progression of chords mirrors the call and response scheme ubiquitous in African and African-American music. During the first decades of the 20th century, blues music was not clearly defined in terms of a particular chord progression. With the popularity of early performers, such as Bessie Smith, use of the twelve-bar blues spread across the music industry during the 1920s and 30s. Other chord progressions, such as 8-bar forms, are still considered blues; examples include "How Long Blues", "Trouble in Mind", and Big Bill Broonzy's "Key to the Highway". There are also 16-bar blues, as in Ray Charles's instrumental "Sweet 16 Bars" and in Herbie Hancock's "Watermelon Man". Idiosyncratic numbers of bars are also encountered occasionally, as with the 9-bar progression in "Sitting on Top of the World" by Howlin Wolf. Like jazz, rock and roll, heavy metal music, hip hop music, reggae, country music, and pop music, blues has been accused of being the "devil's music" and of inciting violence and other poor behavior. In the early 20th century, the blues was considered disreputable, especially as white audiences began listening to the blues during the 1920s. In the early twentieth century, W.C. Handy was the first to popularize blues-influenced music among non-black Americans.
During the blues revival of the 1960s and '70s, acoustic blues artist Taj Mahal and legendary Texas bluesman Lightnin' Hopkins wrote and performed music that figured prominently in the popularly and critically acclaimed film Sounder (1972). The film earned Mahal a Grammy nomination for Best Original Score Written for a Motion Picture and a BAFTA nomination. Almost 30 years later, Mahal wrote blues for, and performed a banjo composition, claw-hammer style, in the 2001 movie release "Songcatcher", which focused on the story of the preservation of the roots music of Appalachia.
Perhaps the most visible example of the blues style of music in the late 20th century came in 1980, when Dan Aykroyd and John Belushi released the film The Blues Brothers. The film drew many of the biggest living influenciers of the Rhythm and blues genre together, such as Ray Charles, James Brown, Cab Calloway, Aretha Franklin, and John Lee Hooker. The band formed also began a successful tour under the Blues Brothers marquee. 1998 brought a sequel, Blues Brothers 2000 that, while not holding as great a critical and financial success, featured a much larger number of blues artists, such as B.B. King, Bo Diddley, Erykah Badu, Eric Clapton, Steve Winwood, Charlie Musselwhite, Blues Traveller, Jimmy Vaughn, Jeff Baxter.