Since officially declaring bandhood around the turn of the millennium, the Bad Plus has convincingly modeled a closed society. Its members -- the pianist Ethan Iverson, the bassist Reid Anderson and the drummer David King -- all hail from the upper Midwest, where they first played together as teenagers. Their chemistry is reactive but stable, and their methods don't avail much room for outside contributions.
But on Tuesday night at the New York Society for Ethical Culture, as part of the JVC Jazz Festival, the group welcomed a rare interlocutor: the guitarist Kurt Rosenwinkel, whose taste for melodic drama and dynamic fluctuation makes him a kindred spirit. The concert felt special, and not just for novelty's sake. As the musicians reached for common understanding, they activated something boundless and radiant within their songs.
