Bebop

Melody - Regular use of the upper notes of the chord, 9ths 11ths 13ths. The semitone approach to the chord note from above in addition to the lead from below. This, of course, led to chromatic chord movements in the harmonies, complicating the sequence but supplying smooth forward momentum. 
The phrasing was 'jagged' and 'angular' and full of fast triplets and sixteenths, the melodic line spiced with unexpected accents.
Harmony - A general trend in 'orthodox' music has been to employ more chord notes - from unison to octaves then fifths and fourths then thirds then more. The same pattern is clear in jazz. Substitute chords were also used to add colour ... again this was nothing new in orthodox music but the Boppers understood why it worked ... it required a better instrumental technique and this provided an elitist impetus to the music
Rhythm - As always in jazz the rhythmic developments were the most important, the subtleties of accent, timing and division of the beat.
The regular four to the bar moved from the bass drum to the ride cymbal to lighten and speed up the beat. The bass drum was effective for accents, 'dropping bombs'. The beat had a better flow.
This was similar to the earlier shift to lighten the beat when tuba and banjo moved to bass and guitar and the high hat complemented the bass drum.
Swing had been dominated by 100 to 200 beats per minute, Bebop went to 300 bpm. At these tempos uneven division of the beat was impossible for all but the most skilled players and strings of even eighths became the norm, reversing one of the earlier innovations of 'swing' ... but Parker did not succumb to the eighth note strings, instead of 'displacing' eighth notes over a single beat as the swing players did, Parker was displacing whole jagged phases away from the beat ... resulting in an extended escape from the ground beat ... this detachment was emphasised by starting and finishing phrases on the 3rd and 4th 'off beats' ... again not a new idea but taken much further by the Boppers ... this sift of time was the main innovation of Bop often making it impossible for 'swing' musicians' to play ... 
Pianists stopped 'comping' the beat and started intermittent 'feeding' the chords to the horns, thus the bass became the mainstay of the rhythm section holding everything together. Horn improvisers now listened to the bass. The bass became the main propulsive force even anticipating the beat. The drums more and more were 'commenting' on the solo line of the horn.

Chronology - Around 1940 Big Band Swing was still going strong but creative musicians were restless. Basie in Kansas City had shown that creative jazz based on the blues was both attractive and popular. Now a second attempt to break from the tyranny and oppression of written commercial swing was made by a group of dedicated and brilliant musicians. They gathered after hours to jam at Mintons in Harlem, simply for the pleasure ... resident were Thelonius Monk and Kenny Clarke but others were soon drawn in - Coleman Hawkins, Chu Berry, Don Byas, Milt Hinton, Charlie Christian, Mary Lou Williams, Lester Young, Ben Webster, Roy Eldridge ... then Dizzy Gillespie, disillusioned within the confines of Cab Calloway's commercialism ... then Charlie Parker, a Kansas blues man hearing and playing things unknown ... free to experiment again ... Bird learns that any note can be resolved from the upper thirds of the chords ... he can fly ... Bird gives the Bebopers phrasing !
After Jay McShann in Kansas Bird joins Dizzy in The Earl Hines Orchestra.
The recording ban (starting in 1942) will make the development of the new Bop something of a romantic mystery even to this day. 
WW2 draft breaks up big bands, opens up competition to new ideas. The country was nervous, and the music was nervous and agitated. Bop became the first jazz style that was not used for dancing. Elitism. 1940 bop innovations. Dizzy deliberately uses major thirds over minor changes in the song Pickin' the Cabbage recorded in May. In June, he uses a diminished 9th on Bye, Bye Blues. These things are new. Charlie Parker, Dizzy Gillespie and Charlie Christian are occasionally beginning or ending phrases on 2nd and 4th beats. This is called "offbeat". The usual practice is to use the 1st or 3rd.
new big band trend is afoot. This trend is called Progressive. Its proponents are Stan Kenton, Boyd Raeburn and Earle Spencer. This will eventually influence what will become Cool Jazz.
1943 Harlem riots, The Savoy closes and jazz moves to the safety of the Westside and 52nd Street - Jimmy Ryans, The Onyx, The Famous Door, The Trock, The Downbeat, Spotlight, Three Deuces, Kelly's Stables ... all styles, Billie and junk prosper ...
1945 after the recording ban Bird's Savoy sides and 'Koko' bursts onto the scene.
1946 Bird in trouble after the Billy Berg gig in LA and Camarillo.
1947 trying to be clean Bird opens at 'The Three Deuces' with Miles Davies.
Everyone wanted to play like Bird.
1949 Bird in Europe is a celebrity but back home he tries to play with Strings great music and more popular but the younger musicians talk of a sell out. Parker was a Blues player.
1949 Birdland opens and although everyone want to play like Bird, a role model with his phasing and unfortunately with his 'dope'. Dope sucked them all dry ... imagine what the music would have been like without 'horse'.
1949 Miles Davis appears as Charlie Parker's trumpet man.
1949 'The Birth of the Cool' with a Gil Evans and a rehearsal band ... cool, soft and intense ... without the virtuosity of Bird, Miles played melodies with timbres ... Gerry Mulligan, Lee Konitz ... J J Johnson and Kai Winding ... but after seeing adulation in Paris Miles became embittered with being a nobody at home and turned to drugs ... 
1954 Bird's daughter dies and accelerates his own rapid demise at 34 years old the following year. On March 4, 1955, Charlie Parker performs in public for the last time at Birdland. On the 12th he dies of heart seizure, haemorrhage, and general bad health. A life unlived. 
1955 'Joyspring' Clifford Brown (1930 -56) and Max Roach - clean brilliance with no hang ups, warm effortless melody, cut short by a road accident.
1956 'Saxophone Colossus' ... was Sony Rollins the natural heir to Bird ? Improvising there and then with a big exaggerated tone and rhythm
Sarah Vaugham - Sassy, rich tone and musical excellence.
The key boppers were Charlie Parker, Dizzy Gillespie, Bud Powell ... but a major contribution to 'Modern Jazz' was made by Norman Granz and 'Jazz at the Philharmonic' - Hawk, Prez, Ella, Gene Krupa, Buddy Rich, Bird, Diz, Stan Getz, Max Roach and Oscar Peterson ... 
Everybody was into Bebop phrasing ... Ella sang it with relaxed ease ... the disciples were - Howard McGee, Fats Navarro, Sonny Stitt, Dexter Gordon, Serge Chaloff, J J Johnson, 
Louis, Billie and Ellington survived Bebop ...
But Bop ran into trouble - it was a musicians music not for dancing - it was undermined by drugs - it was misunderstood by 'hippy' whites - it started to criticise Louis as 'Uncle Tom' - 'mouldy figges' were denigrated 
Jazz is very difficult to play and the mainstream of popular American music goes into the blues stream via - Rhythm and Blues, Soul, Rock 'n' Roll and onto Rock and its derivatives ... 

bebop in the 1940's grew out of the small swing groups, more complex harmonies saxophonist Charlie "Bird" Parker was the father of bebop, also trumpeter Dizzy Gillespie songs by George Gershwin and Cole Porter not intended to be dance music fast tempos based on the chord progressions of popular songs, such as "I Got Rhythm", "Cherokee", or "How High The Moon". The improvisations were based on scales implied by those chords, and the scales used included alterations such as the flatted fifth.
The development of bebop led to new approaches to accompanying as well as soloing. Drummers less bass drum more cymbal and hi-hat. Bass players took over the pulse freeing pianists left hands modern jazz standard form: melody in unison, take turns playing solos, then reunite for melody again
1940-1949 - The 1940's bring even more new styles. Dizzy Gilepsie starts using major thirds over minor changes when he records "Pickin' the Cabbage" in May of 1940. On "Bye Bye Blues" he uses a diminished ninth. Parker and Gilepsie occasionally start and end phrases on the 2nd and 4th beats while the standard beats to end and start on are the 1st and 3rd. It is called playing "offbeat". At this time swing is at its climax but is doomed to fall. Dixieland is being revived and the seeds are being sown the seeds for bebop. Jazz is moving in two distinct, yet opposing directions. One is a New Orleans revival called Dixieland and the other is bebop (also known as rebop or bop) which is born in New York City. At first bop presents relatively few new ideas. Later, eighth notes become straighter in fast songs even though players start playing more off-beat. Also, rhythm changes are bigger. Fast songs become faster while slow songs become slower. Another great achievement of 1941 was when Roy Eldrige joined drum player Gene Krupa's band becoming the first black performer to be accepted into a white big band. In 1942 a recording ban limits the recording of the young bop movement. However, the music is becoming better recognized as a new type of music. The strike ends in 1944. In 1946 the first vinyl record is produced. By '45 the clarinet is nearly out of the picture when it comes to jazz. This is mostly due to the saxophone's influence in the band. Even brass players are forcd to take notice as the sax becomes king. Also by the 1940's, jazz has developed into many different styles of music. Bop, trad, swing, cool, and Dixieland are all being played. Latin music is also influencing jazz.

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