There’s this unwritten rule for contemporary art history students: don’t do a thesis on a living artist, ’cause they’ll contradict you faster than you can say feces-spattered-canvas. So it’s with great caution and wide ambiguity that the Corcoran’s Contemporary (re)defined attempts to organize contemporary work in a large two-part exhibition. This is a buckshot at art related by chronology, with packeted galleries casing recent trends in art like material based abstraction, graffiti, and text or…