“The Greatest Books You’ll Never Read” is a new survey of books that are “unfinished, unbegun or lost, and today exist as only suggestive fragments or not at all.” Despite the title, not all of these works sound particularly great. Take, for example, Karl Marx’s “Scorpion and Felix,” a comic novel he wrote when he was 19 and under the influence of “Tristram Shandy.” According to the Marx biographer Francis Wheen, it’s “a nonsensical torrent of whimsy and persiflage.”

The collection includes several works, like Kafka’s “The Castle” and Truman Capote’s “Answered Prayers,” that were published despite the author’s final intentions being unclear.

Ambitious writers have tried to finish some of these projects (like Jane Austen’s “Sanditon”) over the years, and contributors to “Greatest Books” ponder the odds of other embryonic works being taken up. The prognosticating can lead to incredible acts of understatement, like this take, by the editors, on finishing Saul Bellow’s barely begun novel, “The Crab and the Butterfly”: “Bellow would not be an easy writer to imitate.”

Michael Chabon once wrote 1,500 pages of a novel tentatively titled “Fountain City” before giving up on it. He eventually published four chapters of the manuscript in McSweeney’s, heavily annotated with footnotes that described where and why he had failed. He told The Atlantic in 2010: “The notes are there to serve as the literary equivalent of the label on a packet of silica gel that says DO NOT EAT.”