Blues is based on the use of the minor pentatonic scale with and added blue note. The blue note is a semi tone sharper than the third note of the pentatonic scale that is used depending on key. Major scale is 3 semi tones lower than minor and phrasing of country would be played normally on a major pentatonic scale and blues vocals and accompaniment (melody) are generally
played in the minor blues scale. The rhythmic pattern of the song usually an eight or twelve-bar structure, but there is some variation. Blues is a duet between singer and instrument in a call-and-response manner where the singer sings a line and the instrument (guitar) answers. The use of blue notes and the prominence of call-and-response patterns are typical of the music of West Africa. American blues evolved through spirituals, gospel, field hollers, rhymed Scots-Irish narrative ballads, shouts, and chants. Like the music blues describes being 'down' in spirits, depressed and sad, albeit the phrase also was used as a euphemism for delirium tremens (the DTs) and the police. The blues scale can be found in blues ballads and in conventional popular songs with a "blue" feeling, such as Harold Arlen's "Stormy Weather" and Neil Diamond’s Song sung blue. Slave owners usually allowed their slaves to keep their stringed instruments (many of them had come from Muslim regions of Africa) and they were permitted to play.
Others made a one stringed instrument called the Diddley bow which was based on an African instrument. The Delta Blues technique of fretting the guitar using a knife blade or broken bottle neck corresponds to similar musical techniques in West and Central African cultures. The development of the blues was more or less contemporary with ragtime and jazz, each taking elements of traditional folk music as favoured by the mixed cultures that lived in the south. Blues music was known to exist from the 19th century but the term first appeared in a musical context in 1912, when the first copyrighted sheet music could be bought. At first the works were written by formally trained musicians and the rough elements of country blues were softened with orchestrations, fusing blues with ragtime and jazz. This new sophisticated blues became very popular with white audiences in the 20s and thirties and was performed by female vocalists such as Bessie Smith, and later Billy Holiday. Meanwhile back in Memphis, the Beale Street Blues Clubs saw further developments in grass root blues with many country blues performers like Charlie Patton, Blind Lemon Jefferson, Lonnie Johnson, Son House and Blind Blake encouraged playing and recording their work. At the time, there was no clear musical division between "blues" and "country," except for the race of the performer, and even that sometimes was documented incorrectly by record companies. Gradually this too became popular across America.
During the 1920s and 1930s Delta Blues developed around Memphis, Tennessee and was a rootsy, sparse style music with passionate vocals accompanied by slide guitar. Robert Johnson became the most influential guitarist who bridged both urban and rural blues styles. Not much is known about him other then when he was widowed he decided to become a bluesman. Gigging around the Delta he met Son House and Willie Brown, two stars of the genre, and they were absolutely captivated by his mastery of the guitar. Literally from nowhere he became the bluesman’s bluesman which sparked the myth he had sold his soul to the Devil. (As Faust had done) fuelled by his very famous recordings Crossroad Blues and Hell hound on my trail. In return for his soul he was granted a lifetime of easy money, women, and fame, it was mused Johnstone was so good, the Devil had tuned his guitar as part of the deal. There is an actual crossroads, which is perhaps the most famous landmark in Clarksdale, Mississippi and marks the intersection of Highway 61 and 49. Bowing to popular demand the Mississippi Visitors Bureau marked the "official" crossroads location as the place where the dastardly deed took place but no one is sure. What is certain is Highway 61 and the Clarksdale Railway Station was the way most blues musicians travelled north to Beale Street in Memphis.
Later in the late 30s many blues artists left the city when Mayor "Boss" Crump shut down Beale Street to stop the prostitution, gambling, and cocaine trades. This effectively eliminated jobs for the entertainers and they relocated to Chicago to became part of the urban blues movement, blending country music and electric blues. Muddy Waters, Howlin’ Wolf, Little Walter, John Lee Hooker, and Elmore James among many others continued to play Mississippi Delta blues, backed by bass, drums, piano and occasionally harmonica and this music became very popular in the early fifties. There were two other notables whose impact was to change the face of popular music for ever. B.B. King invented the concept of lead guitar which is now standard in all rock bands; and Willie Dixon, a boxer who could read, write, compose, and arrange music, composed some of the best known delta blues classics which were eagerly recorded by Muddy Waters and Howlin Wolf. The popularity of electric Blues peaked by the mid fifties just before the emergence of Rock’N Roll, however a decade later Delta blues was to inspire the British Invasion and a renaissance in blues music to this day.