"licks" or "riffs"). Sometimes they were entirely original, spontaneous melodies from start to finish. Chord progressions for bebop compositions were often taken directly from popular swing-era compositions and reused with a new and more complex melody, forming new compositions (see contrafact). This practice was already well-established in earlier jazz, but came to be central to the bebop style. The style made use of several relatively common chord progressions, such as blues (at base, I-IV-V, but infused with II-V motion) and 'rhythm changes' (I-VI-II-V, the chords to the 1930s pop standard "I Got Rhythm"). Late bop also moved towards extended forms that represented a departure from pop and show compositions. Bebop chord voicings often dispensed with the root and fifth tones, instead basing them on the leading intervals that defined the tonality of the chord. That opened up creative possibilities for harmonic improvisation such as tritone substitutions and use of diminished scale based improvised lines that could resolve to the key center in numerous and surprising ways. Bebop musicians also employed several harmonic devices not typical of previous jazz. Complicated harmonic substitutions for more basic chords became commonplace. These substitutions often emphasized certain dissonant intervals such as the flat ninth, sharp ninth or the sharp eleventh/tritone. This unprecedented harmonic development which took place in bebop is often traced back to a transcendent moment experienced by Charlie Parker while performing "Cherokee" at Clark Monroe's Uptown House, New York, in early 1942. As described by Parker: I'd been getting bored with the stereotyped changes that were being used, ... and I kept thinking there's bound to be something else. I could hear it sometimes. I couldn't play it.... I was working over "Cherokee", and, as I did, I found that by using the higher intervals of a chord as a melody line and backing them with appropriately related changes, I could play the thing I'd been hearing. It came alive. Gerhard Kubik postulates that the harmonic development in bebop sprung from the blues, and other African-related tonal sensibilities, rather than twentieth century Western art music, as some have suggested. Kubik states: "Auditory inclinations were the African legacy in [Parker's] life, reconfirmed by the experience of the blues tonal system, a sound world at odds with the Western diatonic chord categories. Bebop musicians eliminated Western-style functional harmony in their music while retaining the strong central tonality of the blues as a basis for drawing