The first in the Whitney’s downtown home, this 78th Biennial survey of American art uses every part of the museum’s new capacious quarters. We were fortunate to have a guide who exposed us to artistic thought at several levels — how the museum leverages its structure and location, how it framed this show against current events, and how individual artists comment on current events and social issues. It is not political, just thoughtful. And challenging. It is huge — 66 artists and collectives, “reflecting on the broader cultural concerns of a given historical moment.” It is not a “pretty” show, but an important one that opens the mind. A tour guide is recommended — you won’t get it just looking at the art.