Most of us assume that after a certain age we have to give some things up. Among the comforts forfeited to maturity: chocolate syrup in our milk, training wheels on our bikes, and illustrations in our books. It’s these willful sacrifices that separate the children from the babies. Right?

Not according to grangerizers, those eighteenth-century grown-ups who refused to digest James Granger’s 1769 “Biographical History of England” without pictures. Instead, they launched a movement to self-illustrate the book, inserting mini-portraits of the book’s subjects into their personal copies, handy placeholders to give their imaginations a rest. As the practice spread to other books and expanded in scope—a heavily grangerized book could increase in size many times over—it became the subject of debate. Was grangerizing, or “extra illustration” an “exquisite handicraft” or merely “breaking up a good book to illustrate a worse one?” When it came to the inclusion of non-illustrative elements—playbills inserted into “Romeo and Juliet,” for example—was it ruining a book for the sake of personal recollection, creating a paean to a rotten or sentimental memory? Was it more scrapbooking than art?

In the end, there are good ruined books and bad ruined books, and the quality depends greatly on the artist. It depends a bit, too, on the beholder, and, through May, you can be one at the Folger Shakespeare Library in Washington, D.C., where an exhibit entitled “Extending the Book: The Art of Extra-Illustration” follows the genesis and the controversy of grangerizing. It also provides instructions for how to grangerize your own volumes, which means that you can toil over visually amending your copy of “Pride and Prejudice” with yourself as Lizzie, say, or “Lolita,” with your high-school French teacher as Humbert Humbert, and then you can finally, after all that toil and all these years and with the dignity of an independent adult, sit down with a glass of cereal milk and read a picture book.