Oh, how I love writing in books, and I am afraid I will never really understand the criticism.
Anne Fadiman, in her lovely collection of essays Ex Libris: Confessions of a Common Reader draws a distinction between courtly and carnal lovers of books.
The courtly lover never dog-ears pages, handles books gently so as not to crack the spine, and would certainly never write in a book.
The carnal lover, however, dog-ears, underlines, and loves with abandon. The carnal lover shoves books in back pockets and then cracks the spine bending them back to read one-handed. The carnal lover definitely writes in their books.
I am a carnal lover.
The criticism I hear most often is that I am "defacing" my books. But "defacing" implies a public act — something that ruins the experience of others. One can deface a library book, certainly, just as one can deface a statue or a wall or a building or any other work of art. But a private possession? And in particular, a mass-produced object, the content of which is available extraordinarily widely, and (in the case of classics) freely on the internet? I don't see how any amount of dog-earing, ripping of the covers, highlighting, and marginalia could possibly harm anyone or anything, including the work of literature itself.
But reading with a pen in my hand actively helps me.
I like to think critically about what I read. Sometimes I do read for pure, escapist pleasure. I don't (well, rarely) read Agatha Christie with a pen in my hand. I don't want to dissect her; I just want to read her.
Most anything else I read, though? I want to understand it. I want to follow it. I want to lift the curtain and see how the author is creating their effect (and so when I was trying to write my own murder mystery, I did read Christie with a pen in my hand). I want to retain it, I want to interact with it, and I want to be able to intelligently criticize it. I cannot come up with anything coherent to say about Ulysses without jotting it down (and, honestly, I haven't been — which is why there will be no forthcoming post on Ulysses on this blog!).
Yes, there are other ways I could do this. I could write in a steno notebook. I could take pictures of each section I want to mark, save it in Evernote, and mark up the file (I do something like this for borrowed or library books).
But really, why? It is so inconvenient. The steno pads would mount up. I would have to make an annoying electronic fuss. And then, when I re-read the book, I would have to go back, find the right steno pad or the right evernote file, and match up my notes with the text.
Why on earth would I want to do that when those big, beautiful margins are there, just waiting for me? Writing in books effortlessly connects "my" text with "the" text. It brings me closer to the author and the thoughts of the author. Responding to the text as the story or argument unfolds, I feel as if I am partaking in the "Great Conversation." And partaking in that conversation, even to the smallest extent, is much of what makes me happy in life. (Read this post of mine here on how books help me conquer my existential fear.)
Almost (though not quite) more than helping me connect with the thoughts of the authors, writing in books is like writing a letter to myself. I am a huge re-reader. I love coming across marginalia I scrawled years ago and seeing how my thoughts have changed (or haven't) on the passage. Sometimes I see things totally differently now — sometimes, too, my past self had an insight that my present self has forgotten about that. I do this most, by far, in my Bible, which is a wide-margin Bible specifically designed for this purpose. As I read and re-read my favorite passages, I can see the accretion of my thoughts, growing down the margins. So with my other books, though to a lesser extent.
I also love reading other people's marginalia. A book which has been scrawled in by a famous author dramatically increases in value. I love peeking into such books and seeing what their thoughts were on the matter at hand. I doubt I will ever rise to such prominence that my marginalia will have independent value, but I find that the principle is consistent. I react with glee when I open a used book to find that someone has been there before me. I like to read their insights, too. Apparently Studs Terkel would scold friends if they returned a borrowed book to him without adding marginalia. He told them that reading a book should "not be a passive exercise, but rather a raucous conversation." I agree.
One statement by the anti-writing-in-books set that really sets me off is "I love books too much to ever do that to a book!" Mark Twain was a scribbler-in-books. So were Coleridge, Blake, Darwin, David Foster Wallace, and C. S. Lewis. Are you really arguing that you love and respect books more than they did? Really? Really?
C. S. Lewis, in particular, was an ardent annotator. He had an entire system for his marginalia that he mentioned in one of his letters.
"To enjoy a book like that thoroughly I find I have to treat it as a sort of hobby and set about it seriously. I begin by making a map on one of the end-leafs: then I put in a genealogical tree or two. Then I put a running headline at the top of each page: finally I index at the end all the passages I have for any reason underlined. I often wonder -- considering how people enjoy themselves developing photos or making scrap-books -- why so few people make a hobby of their reading in this way. Many an otherwise dull book which I had to read have I enjoyed in this way, with a fine-nibbed pen in my hand: one is making something all the time and a book so read acquires the charm of a toy without losing that of a book."
In the past my scribbling has been very haphazard, and has often been mainly highlighting passages for easy reference later. Recently, though, I have begun to adopt the C. S. Lewis method: the running header, yes (though not the maps or the genealogical tree), but more importantly the sense of a book as a project. Approaching a book like this gives me an extra zest of pleasure from the book, a pleasure than only compounds itself as I re-read.
So in the end, the more I write in books the more pleasure I get from books. You can pry my pen from my cold, dead, book-loving fingers.