Robert Irwin, perhaps the most influential of the California artists, moved from his beginnings in abstract expressionism through successive shifts in style and sensibility, into a new aesthetic territory altogether, one where philosophical concepts of perception and the world interact. Weschler has charted the journey with exceptional clarity and cogency. He has also, in the process, provided what seems to me the best running history of postwar West Coast art that I have yet seen.--Calvin Tomkins