Venture into the back room of one of New York’s most closely followed art galleries in this week’s episode. David Lewis, the principal and director of David Lewis Gallery in Manhattan’s Lower East Side, shares his optimistic views on the roiling art market, reveals the fault lines among auction houses, mega-galleries, and the rest of the art world, and provides an indispensable primer on the theoretical and ideological underpinnings of contemporary art since the 1970s (bring a dictionary).