A used book with someone’s notes in the margins is a conversation with a stranger who loved the same page.

Marginal notes are one half of an exchange that reaches you years later. Somebody underlined a line, argued with a paragraph, wrote a name beside a passage, all for themselves with no idea anyone would read it, which is why it is honest. You end up with the book and a second reader inside it.

Read the notes as well as the book, especially where they disagree with what you thought. Then write in your own books, properly, in pencil if you are squeamish. A copy you have argued with is worth more than a clean one, and the next person gets two readers.