There are moments when quite separate fragments of information or opinion come together and something hitherto only vaguely intuited becomes clear. Opening a new book called Forgetting by the Dutch writer Douwe Draaisma, I am told almost at once that our immediate visual memories “can hold on to stimuli for no more than a fraction of a second.” This fact—our inevitable forgetting, or simply barely registering most of the visual input we receive—is acknowledged with some regret since we are generally encouraged, Draaisma reflects, “to imagine memory as the ability to preserve something, preferably everything, wholly intact.”

The same day, I ran across a quotation from Vladimir Nabokov on the Internet: “Curiously enough,” the author of Lolita tells us, “one cannot read a book: one can only reread it.” Intrigued by this paradox, I checked out the essay it came from. “When we read a book for the first time,” Nabokov complains, “the very process of laboriously moving our eyes from left to right, line after line, page after page, this complicated physical work upon the book, the very process of learning in terms of space and time what the book is about, this stands between us and artistic appreciation.” Only on a third or fourth reading, he claims, do we start behaving toward a book as we would toward a painting, holding it all in the mind at once.

Nabokov does not mention forgetting, but it’s clear that this is what he is largely talking about. The physical effort of moving the eyes back and forth remains exactly the same on every reading of a book, nor have I ever found it particularly laborious. What is different on a second and subsequent readings is our growing capacity for retention, for putting things in relation to one another. We know the end of the story now and can see how it is foreshadowed at the beginning, how the strands are spun and gathered together. Rereading Mrs. Dalloway, for example, we are struck on the first page to find the comment “What a lark, what a plunge,” of Clarissa’s sallying forth from her house into the street, aware as we now are that later in the book one of the characters will plunge to his death from an upper window. At once we feel we know the novel better, or at least are more aware of its careful construction. It is gratifying.