The history of blues, bebop, and jazz stretches back to African-American slave songs and spirituals about hope amid terrible conditions. In the early 1900s, such songs entered popular culture through ragtime, a style that combined spirituals with marches. Inspired by ragtime, musicians such as Louis Armstrong incorporated improvisation into performances and created a style that came to be known as jazz. Big bands performed throughout the 1920s and '30s to enthusiastic dance audiences, but fell out of favor after World War II. In the 1940s, virtuosic and forward-looking musicians created bebop, a style with a persisting influence in jazz.
Aside from expressing hope in spite of difficult times, blues is a specific song structure, or a variation thereof. The structure is 12 measures long and consists of three melodic phrases and three chords. Any song with this structure, regardless of its instrumentation or lyrical content, is considered blues. Musicians such as Lead Belly, Bessie Smith and Muddy Waters performed songs with this structure. The structure is vital to a substantial portion of jazz, including that performed by Duke Ellington and Charlie Parker.
The question of what exactly constitutes jazz music is contentious among jazz scholars and musicians. However, the term loosely refers to music that incorporates improvisation and has origins in ragtime and blues and any style that stems, directly or otherwise, from the first jazz music. Throughout the 20th century, the term "jazz" has referred to countless disparate styles, especially in the decades after World War II. Previously, "jazz" referred to popular instrumental dance music. After dance bands, known as big bands, were largely dissolved when many of their members were called into military service, jazz generally transmuted from popular music into art music and took various directions.
Musicians in the 1940s developed bebop, a highly virtuosic style of improvising. The term is an onomatopoeic reference to the melodic articulation used in bebop compositions and improvisations. Bebop used conventions of jazz, including the blues song structure. However, Instead of focusing on melodic improvisations over relaxed grooves designed to encourage dancers, bebop musicians emphasized rhythmic and harmonic complexity and often played at very fast tempos. Famous bebop musicians include saxophonist Charlie Parker, trumpeter Dizzy Gillespie and pianist Bud Powell.
The difference between blues, jazz, and bebop is not a question of differing musical styles, but rather a question of intended meaning of the terms. The words are not mutually exclusive but refer to various aspects of a singular, yet broad, American musical tradition.