To really understand hard bop, you have to understand cool jazz. Cool jazz developed as a relatively slow-paced, well-structured, and subdued style of jazz, with a slightly narrow range of emotional expression. Whereas bebop (typified by the music of Charlie Parker, Bud Powell, and Dizzy Gillespie) was fast-paced and full of complex harmony, cool jazz was easy on the ears. The first cool jazz recordings were the Miles Davis Birth of the Cool sessions. Miles Davis wrote of the difference between Birth of the Cool and bebop:
Bird and Diz played this hip, real fast thing, and if you weren’t a fast listener, you couldn’t catch the humor or the feeling in their music.... But Birth of the Cool was different because you could hear everything and hum it also.This was typical of cool jazz as a whole. After Birth of the Cool, other groups adopted the style initiated by Davis and his collaborator, Gil Evans. In addition to incorporating the subtle swing of Birth of the Cool, cool jazz witnessed a rise in experimentation and fusion with the European classical tradition. Gerry Mulligan and John Lewis utilized contrapuntal forms in their music. Dave Brubeck studied composition with the French composer Darius Milhaud and experimented with non-standard meter. These were not the first musicians to engage with the classical tradition (Charlie Parker, for instance, was fond of quoting The Rite of Spring in his solos), but they represented a new wave of experimentation of jazz which was colored with European flavor.
Typically, these Europhilic innovations came at the expense of the various African American cultural forms, such as the blues, which were at the forefront of earlier jazz. Cool jazz also often did not swing as hard as bebop or swing. The lightness of swing and detachment from the blues were major sources of criticism of cool jazz, out of which hard bop was conceived. In a 1986 interview, Art Blakey commented retrospectively that cool jazz was too stale for his taste, alluding to the communicative power he felt in the blues. He charged that the musicians of cool jazz lacked "fire," adding, "Music is supposed to wash away the dust of everyday life, not come in cool. You’re supposed to make [the audience] turn around, pat their feet. That’s what jazz is about." Though he is often credited as a creator of cool jazz, Miles Davis remembered in his autobiography that cool jazz had become unexciting to him by the mid-1950s. He wanted to "take the music back to the fire and improvisations of bebop" after cool jazz had come into vogue in the 1950s.
Hard bop was born in the mid-1950s. Two recordings signaled the birth of hard bop: Miles Davis' Walkin'and Horace Silver's Horace Silver and the Jazz Messengers, both recorded in 1954. The title track of Walkin' was called "the clarion call of the hard bop movement" by jazz critic Frank Kofsky. Written in the traditional 12-bar blues form, the tune featured trumpet playing from Davis heavily versed in the blues and a new approach to jazz piano from Silver, who favored blues voicings over the fugue-like countermelodies of cool jazz. As Davis put it in his autobiography, "I wanted to take the music forward into a more funky kind of blues." Horace Silver and the Jazz Messengers spawned a hard bop classic, Silver’s "The Preacher," highlighted by a gospel-like melody, Silver’s bluesy piano style, and a very strong rhythmic drive.
After these recordings met artistic and commercial success (Walkin’ contributed to Davis’ artistic and commercial resurgence in the middle of the decade while a single of "The Preacher" would sell 100,000 copies), other musicians adopted a similar style, and hard bop as a movement in jazz was born. It was easier to understand than bebop (which was almost universally panned outside of a few enthusiastic critics during the 1940s), but had a stronger rhythmic drive and wider range of emotional expression than cool jazz. Hard bop was funky, earthy, and intensely catchy.
In my mind, the quintessential recording of hard bop was Art Blakey's "Moanin'," written by pianist Bobby Timmons. The melody, laid over a standard 4/4 swing beat, featured call and response riffs between the piano and winds reminiscent of black churches. The tune also featured an incredibly bluesy solo by Lee Morgan, who himself was the archetypal hard bop trumpeter. If you were to construct a checklist of concepts necessary to define a hard bop tune, "Moanin'" would meet all the criteria on the list. The melody swings hard and utilizes blues voicings. The soloists (Morgan, tenor saxophonist Benny Golson, and Timmons) drift between blues riffs and intricate runs of sixteenth notes suggestive of Parker and Gillespie. The arrangement is also well-structured, with the call-and-response patterns and countermelodies explicitly written out for the winds and piano.
The verbal discourse of hard bop was also highly informed by African American culture. "Funky," "dirty," "the gutbucket," and "down-home" came to the forefront of jazz vernacular. Some notable song titles of the style include "Home Cookin'," "Dat Dere," "Dig Dis," and "Sister Sadie." Such descriptions and song titles reflected the African American identity of hard bop.
It is also important to note that hard bop is more accurately a variety of styles united under the term "hard bop," rather than a monolithic and unified style. Nat Adderley's tune "Fun," featured on Cannonball Adderley's Mercy, Mercy, Mercy, rarely gets into 4/4 swing, but it is undoubtedly a hard bop tune. Any of the selections from Charles Mingus' Blues and Roots utilized blues riffs in contrapuntal forms and group improvisation, but the album can still be considered hard bop. Critic David Rosenthal, in his expansive musical study of the genre, divides hard bop into four sub-genres between the poles of experimentally-driven jazz and music that resembles both jazz and R&B. Such a conceptual framework explains why the soul jazz of Ramsey Lewis and the modernist experiments of Mingus can be fit into the hard bop spectrum.
Hard bop was widely praised by a number of critics beginning in the mid-1950s, some of whom had grown tired of cool jazz. Jazz critic Martin Williams praised hard bop’s "return to the roots" of jazz in 1959, arguing that it "saved both the emotional heart of jazz and its very substance from a preciocity [sic], contrivance, and emptiness that certain tendencies in cool jazz might have led to."
Chronologically, hard bop's heyday lasted from roughly the mid-1950s through the early 1960s, but the style itself did not die. Mercy Mercy Mercy, recorded in 1966, is an oft-cited example of the style, while the 1980s recordings of Wynton Marsalis were also arguably hard bop. Certain record labels, most notably Blue Note Records, Prestige Records, and Riverside Records, have become associated with hard bop. While these labels released many hard bop albums, none had a monopoly on the genre, nor were any devoted exclusively to hard bop.