Nokes (Jonathan Swift) claims originality for his new Austen exploration--that it is ""a biography written forwards,"" with ""each moment"" presented ""as it was experienced at the time, not with the detached knowingness of hindsight."" But, he concedes, ""in the disposition of a character's thoughts,... there is some degree of invention."" Austen's abbreviated life, aside from teenage attempts at mocking, in manuscript, the lives she observed, was ""a constant succession of small events"" until she managed to find publishers to chance her writings, first produced for private amusement. By the time Sense and Sensibility emerged in print in 1811, its author was in her late 30s. In 1817, three published novels later, she died, very likely of Addison's disease, an attribution that Nokes buries in the 54th of 81 endnotes in the chapter concerning her death. The author argues with earlier biographers over minor points, describing at length events in Austen's extended family and elaborating on her taste in bonnets and muslins, sponge cakes and dry toast. Such virtuous frugalities overlaid an imaginative life in which the novelist satirically subverted her society. Nokes adds little new beyond his own imagination, which includes entering the minds of his characters and ascribing chicken pox to a decline in health caused by emotional distress. Illustrations not seen by PW. (Sept.) FYI: For another recent biography of Austen, see Valerie Grosvenor Myer's Jane Austen: The Obstinate Heart, reviewed in Forecasts March 10.