I own far more books than I could possibly read over the course of my remaining life, yet every month I add a few dozen more to my shelves. For years I felt guilty about this situation, until I read an article by Jessica Stillman on the website of the magazine Inc. titled “Why You Should Surround Yourself With More Books Than You’ll Ever Have Time to Read.” Stillman argued that a personal library too big to get through in a lifetime “isn’t a sign of failure or ignorance,” but rather “a badge of honor.” Her argument was a variation on a theme put forth by Nassim Nicholas Taleb in his 2007 best seller “The Black Swan,” a book about the outsize impact on our lives of large, unpredictable events. In essence, Taleb claims that although people tend to place a higher value on the things they know than on the things they don’t know, it is the things we don’t know, and therefore can’t see coming, that tend to shape our world most dramatically.

A person’s library is often a symbolic representation of his or her mind. A man who has quit expanding his personal library may have reached the point where he thinks he knows all he needs to and that what he doesn’t know can’t hurt him. He has no desire to keep growing intellectually. The man with an ever-expanding library understands the importance of remaining curious, open to new ideas and voices.

Taleb argues that a personal library “should contain as much of what you do not know as your financial means, mortgage rates and the currently tight real-estate market allow you to put there. You will accumulate more knowledge and more books as you grow older, and the growing number of unread books on the shelves will look at you menacingly. Indeed, the more you know, the larger the rows of unread books. Let us call this collection of unread books an antilibrary.”

I don’t really like Taleb’s term “antilibrary.” A library is a collection of books, many of which remain unread for long periods of time. I don’t see how that differs from an antilibrary. A better term for what he’s talking about might be tsundoku, a Japanese word for a stack of books that you have purchased but not yet read. My personal library is about one-tenth books I have read and nine-tenths tsundoku. I probably own about 3,000 books. But many of those books are anthologies or compilations that contain multiple books within them. I own a lot of Library of America volumes, a series that publishes the complete novels of authors like Dashiell Hammett and Nathanael West as a single book. Thus, my 3,000-book library probably holds more than 6,000 works. Once I have read a book, I often give it away or trade it in at a used-book store. As a result, my tsundoku is ever expanding while the number of books in my house that I have read remains fairly constant at a few hundred.

In truth, however, the tsundoku fails to describe much of my library. I own a lot of story collections, poetry anthologies and books of essays, which I bought knowing I would probably not read every entry. People like Taleb, Stillman and whoever coined the word tsundoku seem to recognize only two categories of book: the read and the unread. But every book lover knows there is a third category that falls somewhere between the other two: the partially read book. Just about every title on a book lover’s reference shelves, for instance, falls into this category. No one reads the American Heritage Dictionary or Roget’s Thesaurus from cover to cover. One of my favorite books is John Sutherland’s “The Stanford Companion to Victorian Fiction.” It’s a fascinating, witty and very opinionated survey of Victorian England’s novels and novelists, from the famous (Dickens, Trollope, Thackeray) to the justifiably forgotten (Sutherland describes the novels of Tom Gallon as “sub-Dickensian fiction of sentiment and lowlife in London, typically written in an elliptical, rather graceless style”). I’ve owned the book for 20 years and derived great enjoyment from it, but I doubt I’ll ever manage to read every word of it or of dozens of other reference books on my shelves.

Nor do I typically read biographies all the way through. Biographers have a tendency to shoehorn every last tidbit of information they can into their books. I don’t really care about the marks that Ogden Nash received on his third-grade report card or how many trunks of clothing Edith Wharton had shipped across the Atlantic when she moved to France. There are probably hundreds of biographies in my personal library. I have read parts of most of them but I have read very few in their entirety. The same is true of collections of letters. Whenever I finish reading a work of fiction by, say, Willa Cather, I’ll be inspired to pull out the massive tome “The Selected Letters of Willa Cather” and try to get the measure of what the author was like when she was “off duty.”

These cannot be counted as books I have read, but nor can they be labeled tsundoku. Like much of my library, they live in the twilight zone of the partially read. Taleb argues that “read books are far less valuable than unread ones,” because unread ones can teach you things you don’t yet know. I don’t really agree with him. I think it’s a good idea to keep your shelves stocked both with books you’ve read and books you haven’t. But just as important is that third category of book: those you haven’t read all of and may never get around to finishing.

The sight of a book you’ve read can remind you of the many things you’ve already learned. The sight of a book you haven’t read can remind you that there are many things you’ve yet to learn. And the sight of a partially read book can remind you that reading is an activity that you hope never to come to the end of.

Perhaps the Japanese have a word for that.