Most people treat books like delicate objects. They keep them clean, pristine, and absolutely unmarked. A creased spine feels like a wound. A note in the margin? Unthinkable.
But in 1940, a man named Mortimer Adler said this attitude was nonsense. His short essay entitled How to Mark a Book argued that writing in your books isn’t defacement — it’s a sign of life. The only way to really understand a book is to engage with it, argue with it, and respond to it.
Today, science backs him up. Studies in educational psychology show that annotating a text dramatically improves your retention of its contents. In some cases, readers who engage actively with what they read by marking a book remember up to seven times more than those who don’t.