The title of the speech was “At the Same Time: The Novelist and Moral Reasoning,” and in addition to offering an appreciation of Gordimer’s writing, it was a long reflection on the nature of narrative in general.

It was her last speech, and at the beginning of a book of Sontag’s essays published posthumously in March of this year, the editors explain that this book of essays had had no working title, and that they had decided upon the title At the Same Time: Essays and Speeches for the whole collection; the speech forms the last chapter of the book and had never before appeared in print.

On April 20, the Times Literary Supplement published a short letter to the editor, written by John Lavagnino, a senior lecturer in humanities and computing at King’s College London.

Mr. Lavagnino has read a review of At the Same Time, and particularly noted its treatment of Sontag’s passage on “hyperfiction.”

“Sontag most likely never read any hyperfiction at all,” he wrote, “because her account of what it is derives, without attribution,” from a March 1998 New York Times Book Review column by Laura Miller.

While it seems impossible from reading Ms. Miller’s 1998 Book Review piece and Sontag’s essay to conclude how much hyperfiction Sontag had read, Mr. Lavagnino’s observations about the similarity between the two pieces does to hit the mark.

“Shortly after personal computers and word-processing programs became commonplace tools for writers, a brave new future for fiction was trumpeted,” Ms. Miller had written in the lead of her New York Times Book Review piece.

“Ever since word-processing programs became commonplace tools for most writers—including me—there have been those who assert that there is now a brave new future for fiction,” were the words Sontag delivered in the 2004 lecture.

Ms. Miller also wrote: “Hypertext is sometimes said to mimic real life, with its myriad opportunities and surprising outcomes …. ”

Sontag wrote: “Hyperfiction is sometimes said to mimic real life, with its myriad opportunities and surprising outcomes …. ”

Neither of these borrowings would seem to cut to the bone of the essay, which asserts that the novelty for overthrowing the author—and, more profoundly, the constraints of time and space that bind a book made of paper—does an injustice to writing at large.

But there’s more:

“People who read for nothing else will read for plot,” wrote Ms. Miller, “yet hyperfiction’s advocates maintain that we find it ‘confining’ and chafe against its ‘limitations.’”

“People who read for nothing else will read for plot,” wrote Sontag. Then, in beginning a new paragraph, she continued: “Yet hyperfiction’s advocates maintain that we find plot ‘confining’ and chafe against its limitations.”

There is, in the Sontag essay, no attribution to Ms. Miller or The Times. And no quotation marks are used in preceding passages that are not reproduced here, either.

“Although the whole speech isn’t a commentary on hypertext,” said Ms. Miller in a phone interview, “the part of it that borrows so much from my piece is a commentary.”

Mr. Lavagnino said he first sensed something strange in the Sontag lecture when he recognized a quote from the French theorist Roland Barthes’ famous book S/Z, presented without attribution, in the piece (which was printed in The Guardian March 17 under the title, “Pay Attention to the World.”)

“It has no beginning; it is reversible; we gain access to it by several entrances, none of which can be authoritatively declared to be the main one,” the Barthes quote reads. In Ms. Miller’s piece, it was attributed to Barthes, but in the Sontag essay, no words or quotation marks attribute the quote to anyone but Sontag herself.

Finding the earlier use of the quotation in the piece by Ms. Miller, Mr. Lavagnino discovered further similarities between Ms. Miller’s work and the essay by Sontag.

Ms. Sontag also quotes metafictionist Robert Coover—author of The Public Burning, among other novels, and another writer mentioned in the Miller piece—without any attribution.

What had most puzzled Mr. Lavagnino, by his account, was that Sontag was arguing against hypertext in 2004. Hadn’t that academic debate already fallen totally out of vogue even by the time Ms. Miller was writing in The Times in 1998?

After the letter was published, James Campbell, a TLS assistant editor who writes the Nota Bene column, sent it along to Dwight Garner, a senior editor at the Times Book Review. Mr. Garner passed it along to Ms. Miller.

Had the publisher, Farrar, Strauss & Giroux, followed the conversation about the origin of the Sontag essay?

FSG president Jonathan Galassi said he hadn’t seen the TLS letter, but would consult the book’s two editors, Paolo Dilonardo and Anne Jump.

“This was a speech, not a formal essay,” Mr. Galassi wrote in an e-mail to The Observer, in which he also acknowledged he had not been able to ask the book’s editors anything about the manuscript they were working from.

“Susan herself never prepared it for publication,” he wrote. “I’d say it’s certainly legitimate in a speech to quote others without mentioning them by name in that kind of context—the point was the nature of the argument, not the makers of it, and she does put the quotations in quotes. If it turns out that she did actually borrow directly from Laura Miller, we will certainly add a note to this effect in future printings.”

Sontag’s surviving son, the journalist and writer David Rieff, wrote the book’s foreword, but couldn’t be reached for comment before press time.

Adrian Tahourdin, the TLS’s letters editor, said that he didn’t compare the Sontag and Miller texts before running the letter, as is the publication’s policy. And, since then, he has not received any complaints from other readers.

Upon reading the TLS letter, Ms. Miller said she initially thought that Sontag “lifted my research”—committing what might amount to a literary misdemeanor. “When I actually sat down and read it,” she said, “it was more than that.”

Ms. Miller, who read the Sontag lecture in a bookstore last week and is admittedly “not a huge Susan Sontag fan,” left the book on the shelf.

“The kind of irony is that it was in a lecture on morality and literature,” she said.