In describing his work, the late Richard Artschwager would simply say, “If you sit on it, it’s a chair. If you walk around it and look at it, it is a sculpture.” He was interested in the in-between and his oeuvre of sculpted books, clocks, stairs, and punctuation marks avoids categorization, existing somewhere between Pop Art, Conceptual Art, and Minimalism. In this rare exhibition, works from the first two decades of his career, 1964 to 1987, are on display. —E.C.