This new volume in the Documents of 20th Century Art series, under the general editorship of Robert Motherwell and Bernard Karpel, pulls together the writings, many previously unpublished, of the late Ad Reinhardt, artist and iconoclast whose completely black canvases are now recognized as preceding minimal art by twenty years. First exhibited in the '50's when modern American art was changing its representational face into the pop-op-surreal-abstract expressionist styles we readily accept today, Reinhardt's ""empty"" paintings had to be roped off in exhibition to avoid defacement by a public willing to be shocked only so far. Rose, the art critic for New York and Vogue, introduces Reinhardt as a happy combination of articulate theoretician and creative forerunner. A one-time editor of his college humor magazine, he is succinct, quotable, delightfully irascible. His work developed gradually into monkish academicism influenced by Oriental philosophy. His emphasis on ""morality"" verged on the obsessive. He increasingly styled himself as gadfly and purifier of the art world, with its ""Bedlam of half-baked philosophies and cockeyed visions,"" and more important, its ""Barnumism."" In his own words: ""Art is art. Everything else is everything else""; ""Art is too serious to be taken seriously""; ""Up your crass-materialism."" Which doesn't begin to do justice to his self-irony, his involuted send-ups of critical mumbo jumbo, or his playful intelligence. Certainly not for everyone, but a touchstone in sorting out the direction of postwar art in America.