Editor's note: CNN contributor Bob Greene is a best-selling author whose new book is "Late Edition: A Love Story."
(CNN) -- So I'm studying a menu, sitting at the bar of a restaurant on a recent trip, and two couples arrive for dinner. They ask if the bar stool next to me is taken.
I say it isn't, and one member of their party sits down and they continue their conversation. One of the voices sounds startlingly familiar. It's a great voice --authoritative, inviting, cultured without being aloof. It's a voice that sounds as if it should be narrating "American Experience" documentaries on PBS, or maybe films by Ken Burns.
I turn to see who has such an enviable voice, and it's no coincidence that I associated it with "American Experience" and Ken Burns, because the owner of the voice is the superlative historian David McCullough, twice winner of the Pulitzer Prize, author of "John Adams" and "1776" and narrator, indeed, of all those "American Experience" and Ken Burns programs.
We'd never met, but we start talking -- you feel like you want to lasso that voice and keep it in a bottle for when you need it on a cold winter night -- and McCullough turns out to be just as good a guy as you'd hope. Of all the things I might ask him about his books, the first thing I say has nothing to do with a single word he has written.
"Mort Janklow always says that the jacket of your Truman book is as effective a book cover as he has ever seen," I say.
"I know," McCullough says.
Janklow is McCullough's longtime literary agent, and he understands what is likely to make a customer in a bookstore stop in the aisle, pause before a book, pick it up and, if the stars are aligned ideally in the heavens, take it home and read it.
"Truman," which was published in 1992, features a humanizing pastel portrait of Harry Truman in profile, set against rural fields that make the whole presentation feel like a balmy and sun-dappled American afternoon in summer.
If, before McCullough's biography, the visual image of Truman in the public's mind was harsh and starkly shadowed and black-and-white, the book jacket, painted by Wendell Minor, went brilliantly against expectation. Full of soft greens and blues, in a single glance it made Truman suddenly seem accessible, a fellow with whom you'd like to sit down for a glass of lemonade. The biography was an enormous best-seller, and that book jacket had a lot to do with getting people into McCullough's tent.
We talked about various other things, and a few days later there appeared in The New York Times a story by reporter Motoko Rich under the headline: "In E-Book Era, You Can't Even Judge a Cover." Her thesis was that as more and more people become accustomed to reading books on small screens, the importance of book jackets could rapidly diminish. As she wrote: "You can't tell a book by its cover if it doesn't have one."
Books still have covers, of course; even as the digital era gallops along, publishers continue to design and print jackets for their books, which then become the books' logos in their electronic versions. Yet if we do reach a time when the great majority of books are read on the screens of portable devices, something will be lost.
It goes beyond the marketing value of book jackets. Rich concentrated on that aspect in her story, pointing out that people see other people reading books in public and are sometimes inspired to give the book a try. You can't do that so easily when someone is peering down at an e-book on a small screen.
Yet there is also a sense of ownership that a book jacket bestows: A book is an object, a thing, and it becomes a lovely one, almost a piece of art independent of the words, when the jacket is evocative and illuminating.
If you have books in your home, you can probably close your eyes and visualize the jackets of the ones you love best. If and when that goes away -- if the majority of the books you buy are not kept on shelves in your home but stored in your digital reader -- that will disappear. Not completely; the analogy is to old record albums. The album covers were artwork that you possessed; you didn't buy the music because of the covers, but the covers became a part of your world. They lived with you. You couldn't think of the songs without thinking of the covers of the albums.
When CDs replaced vinyl albums, the cover art grew much smaller; it still existed, but it seemed not quite so significant. You can see record-album covers on your computer or phone whenever you want, along with videos of the bands performing some of the songs. We are awash in images, available with a click. But somehow they lack the staying power of that single, static design that was created for a sole purpose: to be the eternal public face of the music.
Same with book jackets. The existence of a gorgeous jacket amplifies the truth that a book is not, or at least should not be, disposable. It is a part of your life that is there for the long run. You might not read a book a second time, but its jacket wrapped around it, sitting in your home, is a reminder of certain things: what you were going through as you first held it, who in the world was important to you, how the words on those pages made you feel.
You can't judge a book by its cover, but you can judge a book cover. And the best of them become as vital a part of a book as the sentences on the bound pages.
Or so I said to Mr. McCullough, whose voice is a book jacket of its own, heralding what is inside. But let's not get too carried away here. We shared a drink and spoke about the power of words.
The opinions expressed in this commentary are solely those of Bob Greene.