I never write in a borrowed book whether it is from the library or from a friend. But, if the book is mine, I fill the margins with my thoughts, impressions, wonderments and questions. My Bible is the best example with notes, definitions of words or an expanded definition the illuminates the meaning of the passage, spiritual discoveries and dates. It is my personal faith journey history. For me, any book that is used for study, is fair game when it is in my hands. Writing in my books helps me retain the content of the book. Few novels get any margin comments because for me, they are for pure pleasure reading not study.
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