I have a grandmother I idealize.
She died of lung cancer two years before I was born, and is the only grandparent I never knew. I didn't miss her until I became a teenager and started actually noticing her books in my grandfather's study. Books on Eleanor of Aquitaine, books by Trollope (whom I still haven't read), books on the history of Africa.
My grandfather died when I was 14, and I asked for and received my grandmother's books, most of which have stayed at my parents'. The only ones I decided to bring to Chicago with me when I moved at age 22 were two of her textbooks from college. One is a book of Spenser's poetry, the other is Milton. I hate both of those men, but I love that she wrote in their books. It's mostly the kind of idiotic notes you take in freshman year lit classes, but occasionally there're things like this:
Because people don't only doodle in the 21st century.
One of the only personal notes I could find was this in the upper right-hand corner:
And it completely delights me. How diff from Shaw indeed, Grandma Jean.
One of the strongest cases I can think of for writing in books is the link it gives you with the future. I can only hope my copy of The Mystery of Edwin Drood survives so that my theoretical granddaughter can read my "Gross" and "sleepovers are the same forever" commentary. My copy of The Golden Bowl has a note from 15-year-old me at the beginning saying "Abandon hope, all ye who enter here;" my copy of Harry Potter and the Goblet of Fire was written in by my oldest brother, saying 'To one of my favorite Muggles;" and I fully intend on penning something to future generations informing them that the copy of Bleak House that they hold in their hands has been hugged well beyond an acceptable number of times.
The books people keep, and maybe write in, and decide to truck with them from home to home, can be the things that show you who they are — or were. Those books can help you feel a closeness to their owners that you wouldn't be able to achieve otherwise. My grandmother, it turns out, loved Jane Austen. How much time could we have spent debating whether Persuasion holds up well to a second reading? (I'm going to go with 'too much,' no matter how long) She could have told me her favorite Trollope, and which was the best to start with. She could have told me why she loved Eleanor of Aquitaine so much. I don't know, and it bothers me. But I'm glad I know she did.
1933 Jean Brandon. You will meet and marry a man named Joe who will love you forever, and you will have a son who loves rockets and outer space. He will marry a woman who is an actress and a writer, and their weird combination will give you a granddaughter you will never meet, but who thinks your taste in books is fabulous.
And keep going with the Milton. It eventually ends.