You see it everywhere, even if you don’t always recognize it: the literary allusion. Quick! Which two big novels of the past two years borrowed their titles from “Macbeth”? Nailing the answer — “Birnam Wood” and “Tomorrow, and Tomorrow, and Tomorrow” — might make you feel a little smug.

Perhaps the frisson of cleverness (I know where that’s from!), or the flip-side cringe of ignorance (I should know where that’s from!), is enough to spur you to buy a book, the way a search-optimized headline compels you to click a link. After all, titles are especially fertile ground for allusion-mongering. The name of a book becomes more memorable when it echoes something you might have heard — or think you should have heard — before.

This kind of appropriation seems to be a relatively modern phenomenon. Before the turn of the 20th century titles were more descriptive than allusive. The books themselves may have been stuffed with learning, but the words on the covers were largely content to give the prospective reader the who (“Pamela,” “Robinson Crusoe,” “Frankenstein”), where (“Wuthering Heights,” “The Mill on the Floss,” “Treasure Island”) or what (“The Scarlet Letter,” “War and Peace,” “The Way We Live Now”) of the book.

Somehow, by the middle of the 20th century, literature had become an echo chamber. Look homeward, angel! Ask not for whom the sound and the fury slouches toward Bethlehem in dubious battle. When Marcel Proust was first translated into English, he was made to quote Shakespeare, and “In Search of Lost Time” (the literal, plainly descriptive French title) became “Remembrance of Things Past,” a line from Sonnet 30.

Recent Proust translators have erased the Shakespearean reference in fidelity to the original, but the habit of dressing up new books in secondhand clothing persists, in fiction and nonfiction alike. Last year, in addition to “Birnam Wood,” there were Jonathan Rosen’s “The Best Minds,” with its whisper of Allen Ginsberg’s “Howl,” Paul Harding’s “This Other Eden” (“Richard II”), and William Egginton’s “The Rigor of Angels” (Borges). The best-seller lists and publishers’ catalogs contain multitudes (Walt Whitman). Here comes everybody! (James Joyce).