Christened in 1967, the flagship of the AACM this year sailed into its fourth decade, albeit with fewer scheduled departures: no longer the primary occupation of its members, the AEC reassembles but several times each year, and by my reckoning, it has played its hometown only twice this decade. When reedists Roscoe Mitchell and Joseph Jarman, trumpeter Lester Bowie, and bassist Malachi Favors first formed the Art Ensemble–“of Chicago” came soon after, courtesy of a Paris concert promoter–I doubt they expected to be together in 1997, but the full-force percussion of drummer Famoudou Don Moye, who joined in 1969, transformed the music and undoubtedly helped insure the band’s longevity. Over time the AEC has lost the ability to outright shock an audience–the circus theatrics, sound effects, furious polyphonic solos, and extended tone poems were institutionalized as far back as the early 80s, when the group began recording for ECM (a paragon of decorum). But it retains the knack for making the most abstract musical elements concrete and even funky, and just the presence of Mitchell and Bowie–two of the most distinctive instrumentalists of the postbop era–guarantees a basic level of excitement. For some time now, Jarman–who also served as the AEC’s poet and spiritual adviser–has committed himself completely to other enterprises, leaving the band to work as a quartet, and over the last few months, a serious illness has forced Mitchell to cancel some appearances. The potent and popular Chicago sax man Ari Brown took Mitchell’s place, leading to speculation that he might remain in the group when Mitchell came back, thus restoring the band to a quintet. But with Mitchell’s return, Brown is back on the bench. Monday, 7:30 PM, main stage, Steppenwolf Theatre, 1650 N. Halsted; 312-335-1650. NEIL TESSER

Art accompanying story in printed newspaper (not available in this archive): uncredited photo.