The publication of a still-living writer’s diaries suggests that their author is a possessor of such effortless, commanding genius that even his private, incomplete thoughts must be made immediately and copiously available to the reading public. That such an honor should fall to Joyce Carol Oates — whose reputation, timeworn though it now is, could not even at its height justify such an unveiling — is somewhat mysterious. Not unprecedented — the diaries of the minor poet May Sarton, after all, have seen the light of day, as have Edmund Wilson’s transcriptions of his senescent lusts — but nonetheless puzzling.

So it is heartening to say that “TheJournalofJoyceCarolOates” (Ecco, 509 pages, $29.95) will both delight and instruct readers — or at least those readers who find high good humor in the joyless narcissism and garrulous metaphysical speculation which constitute Ms. Oates’ natural register as a diarist. This is to say nothing of the unintentionally hilarious throwaway lines (in December 1976, Ms. Oates asks, in schizoid all-caps, “WHY AM I SO REASONABLE, SO EVERLASTINGLY SANE”) with which the hefty book is liberally salted. But to those looking for the usual excellences of a writer’s diaries — penetrating analysis of the writer’s own work and the work of artists he admires; aid in understanding the writer as a personality and his work as a whole; witty or vicious remarks and gossip — the “Journal” will prove a wasteland. And this despite the fact that Oates the diarist is just as mechanically fluent as Ms. Oates the novelist: In 495 pages the “Journal” covers the spanofonlynineyears. (The book’s editor, Greg Johnson, informs us in the foreword that the present selection has been culled from 4,000 single-spaced typewritten pages, housed in an archive at Syracuse University.)

The novels, stories, criticism, and essays Ms. Oates was writing and editing during the span the “Journal” covers occupy a large part of Ms. Oates’s mind and of the diary itself, which is understandable. But the droning, self-infatuated way in which she has chosen to write about her own work — “Doing galleys of Son of the Morning. The first two chapters I found very moving, in fact I began to tremble while reading them…” is one typical reflection; “Working on Jigsaw. Absolutely enchanted with the development of the characters…” is another — should render those sections completely devoid of value even for the most passionate admirers of her fiction, whom one assumes are the main audience of the “Journal.” (Less charitable readers might see Ms. Oates as guilty of a charge she lays at the feet of the poet John Berryman: “myopic self-praise.”)

Oates’s more naked moments of introspection are similarly cringe-inducing. Pondering Jungian thought, she gives us “What relationship does the myth have with one’s true self? Is there a true self? I feel, at times, so unutterably bewildered…!”; contemplating (apparently) the idea of the eternal return, she comments: “…Life the immense wheel, grinding, moving. Rolling. Placid as a cow chewing its cud. I curl back upon myself, discover earlier selves—the same thoughts—the same revelations!” Gentle meanderings such as these, which may be found consistently throughout the “Journal,” make the book read as though it had been written by a vicious misogynist, parodying the inner workings of the feminine mind. And insofar as Ms. Oates has reduced these paths of thought to their most generic forms, they also cannot help but make the reader suspicious that she recorded them with an anticipatory eye to their being eventually published: it’s hard to imagine anyone’s inner life assuming such clear, unobjectionable contours.

All this aridity is not even relieved by any decent (let alone noteworthy or salacious) literary dish. About the best Ms. Oates can do in that department are monochromatic transcripts of endless, “lovely” (a word that appears with frightening frequency in the”Journal”) lunches, dinners, and cocktail parties: “almost too much is happening: Monday, a lovely luncheon with Stanley Kunitz and his wife…Today, a prodigious four hours: Gail Godwin, Robert Starer, Ed Cone, George Pitcher for luncheon…I served Stanley Kunitz’s 10-surprise soup as a first course…” It’s kinder, probably, to leave off excerpting here.

So we see that the publication of this book, far from clarifying anything about the nature of its author’s work, deepens the mystery surrounding her once-high reputation. How could a mind of such a common, even vulgar stamp — a sensibility fond of the word “lovely” and of ponderous, empty philosophizing — ever have exercised any literary sway among the higher brows, as it very much did in the ‘70s and ‘80s? (Perhaps precisely because it is so innocuous, so anodyne, despite the portentously dark themes of Ms. Oates’s novels.) A great many artists have revealed themselves as vicious, vain, satyr-like, obsequious, even monstrous in their private journals. But few have so candidly brought to light their blandness and triviality. The “Journal,” in the end, may be the single best riposte to Gore Vidal’s oft-repeated crack that the three saddest words in the English language are “Joyce Carol Oates”: there is not enough substance here even to qualify as sad.

Mr. Munson is the online editor of Commentary.