When about 200 books from Franz Kafka's private library turned up recently in the hands of a Munich bookseller, first reports indicated that the volumes were unmarked by marginal notes or underlining. Professor Jurgen Born, a Kafka scholar on the faculty of Prague's University of Wuppertal, observed: ''I would not expect annotation. That's not the way he had with books.'' And indeed it does seem fitting that the author of such spare fantasies as ''The Castle'' and ''The Metamorphosis'' should be as austere with his books as he was with his life.
For most readers, an unmarked book is as unnatural as a sofa without an imprint on the cushions.
One possesses one's books officially by underlining them.
One makes reading an active rather than a passive pleasure by those little scribbles in the margin.
The reader is a collaborator. The book that I read becomes a different work from the book that you write because of what I see (and don't see) in it; and that perception itches to be recorded. Marginal notes, and even underlining, are tangible proof that the reader is also a writer, or at least an editor, italicizing favorite passages.
That somewhat grim Victorian, John Ruskin, made reading a form of hard labor. The reader with marking pencil and straightedge in hand should ask himself, according to Ruskin, ''Am I inclined to work as an Australian miner would? Are my pickaxes and shovels in good order, and am I in good trim myself?''
Ruskin's athletic approach is meant to get the supine reader off his pillows and into the proper adversary posture. Any borrower of library books knows that the commonest inscription in the margin is, ''How true!'' This seems to hold, whether the work is a novel by Jane Austen or a history of the Eskimos. Ruskin had specific warnings against the practice. An annotating reader, he instructed, should never write in the margin, ''How good this is - that's exactly what I think!''
Your model Australian miner, he advised, would jot down: ''How strange that is! I never thought of that before.''
For readers with writer's block, the Irish wit Flann O'Brien suggested a service, pre-underlining no less than 50 percent of a new book in ''good-quality red ink,'' with appropriate phrases to be selected by the customer, such as: ''Rubbish!'' Or, ''Yes indeed!'' Or, ''But why in heaven's name?''
Obviously the writers of marginal notes are authors of sorts in search of readers themselves. A witty - or cleverly indecipherable - annotator can divert a subsequent reader so that he pays more attention to the margins than to the print. Reading then becomes a slightly eerie experience, like getting your telephone line plugged into an invisible somebody's intimate conversation.
The reader can feel the same effect, opening books marked by his own hand years ago.
Some underliners, particularly when students, work out elaborate codes. Red pencil means, ''Important - essential.'' Blue pencil means, ''I just happen to like this.''
Or is it the other way around? And what do those double vertical marks in the margin signify? And why did one underline in certain places and enclose passages in brackets elsewhere?
Twenty years later, who knows what this stranger - this younger self - wanted? It's like confronting an old lock for which one has forgotten the combination.
As for the ''How trues!'' of 20 years ago, how embarrassing!
Is this what Kafka knew? - a man who wished his own writings destroyed. A man who understood how revealing any writing can be, even in the margin of another writer's book.
Still, the urge to make a mark in a book is nearly irresistible. As an article of faith, all annotators must believe that somewhere in the white spaces of those 200 volumes Kafka could not keep from recording at least one solitary response. And he was right - that single pale scrawl, asserting, ''I mark, therefore I exist,'' will tell all.