Newer theories of the universe notwithstanding, the writing of nonfiction is about being honest and about being the sort of person (both writer and subject) whose truth is interesting enough. These are the plain unglamorous facts responsible for the pleasure of Lawrence Weschler's classic biography of Robert Irwin—newly updated in a second edition, with about 80 more pages (some published previously, some not)—and his new biography of David Hockney.

The publishing of these two new books, pitched to the reader as companions despite (and because of) the fact that Irwin and Hockney believe each other to be dead wrong about everything, was a delicate matter. It could have been the occasion for a mucking up of a good thing. That good thing, that very good thing, is Seeing Is Forgetting the Name of the Thing One Sees, the original Irwin book, a slender and perfectly nondefinitive volume that nevertheless became the book to read if you are only going to read a single book about art in the 20th century. But Weschler had to do it.

For starters, his subject—Irwin—radically changed direction just as the first edition came to its close. Over 25 years, Irwin's work had performed a gradual disappearing act, going from expressionistic painting to see-through scrims hung in galleries that often went entirely unnoticed, but what came next, unthinkably, were massive, multimillion-dollar public projects. Irwin had jumped off the ledge into what Weschler called "zeroland" all right, but "Let's just say I hit an outcropping about 10 feet down," Irwin told his biographer, who gives us the momentary sense of Irwin as a gleeful cartoon character about to zip off and away again.

Weschler, to his eternal credit, is unfazed by this sort of thing. In fact, he seems to prefer following the winding line of an unruly subject. In these newer essays, Weschler challenges his subject. (How can you show drawings for unbuilt proposals when your work is about direct experience? Why do a retrospective—is it your ego?—when so much of your art doesn't exist anymore or can't be transplanted from where it lives? What on earth are you doing building a garden for Richard Meier's Getty?) And he is dumbfounded when Irwin shares a near-death experience that the artist never bothered to mention in the two decades of interviews that came before. It's great eavesdropping, and at the same time the historical record is fattened, too: Weschler's description of Irwin's role as lead designer for Dia:Beacon has never been laid out this clearly before.

When Seeing Is Forgetting came out, Weschler writes, Hockney disagreed with everything in it and invited Weschler to hear him out. The hearing out has become the book True to Life: Twenty-five Years of Conversations with David Hockney, during the making of which Weschler exacts revenge (it is a good-natured vengeance: he loves these men) on his subjects—who have never met—by noticing that their explorations are actually "entirely convergent and indeed now virtually congruent."

If Irwin's story is about unframing the art object to the point where it becomes part of the world and vice versa—essentially training people to expect art everywhere—then Hockney's story is about reversing the Renaissance and restoring human vision to its rightful place in the body, a body that not only has two eyes instead of the camera's one but that also is constantly moving as it looks, zooming and pulling away and never losing the periphery, never framing in the first place.

Hockney is obsessed by these ideas, as we all know from his big, beautiful 2001 book Secret Knowledge, in which he makes controversial claims about old masters using optical devices, but it's Weschler's little paperback that explains Hockney's arcane tome. While everyone else was trying to track down whether Hockney was right (they still don't know), Weschler was doing something much more interesting, as usual. This final biography, beginning with Hockney's little-considered Polaroid collages of the 1980s and culminating in Hockney's huge gridded forest portraits of last year, is like a vast tract of land that leads outward in all directions. (It takes Weschler precisely one move to get from Wagner to his great-grandmother's orgasms, and from the left hand of Caravaggio's Bacchus to the early Christian church's definition of heresy.) After a certain amount of reading Weschler, one realizes that this vast, pumping landscape is simply where he lives. To visit is to experience a place that seems bigger and better but is no different from every other place. With his words running through you, it's you that's different. recommended