What is Marginalia?
Marginalia are the notes, marks, and commentary a reader writes in the margins of a text. More than decoration, they are a record of a mind responding to an author in real time. H. J. Jackson's history of the practice traces three centuries of readers writing back to their books.
Jackson's study, based on thousands of annotated books, shows marginalia ranging from quick marks of emphasis to running arguments with the author, and treats them as evidence of how reading actually happens: actively, socially, and often combatively. Annotated copies circulated among friends, and some readers, famously including Samuel Taylor Coleridge, were asked to annotate books precisely because their marginal notes were valued.
As a learning practice, annotation converts reading from reception into dialogue. Writing a response, an objection, or a summary in the margin is generation, and deciding what deserves a mark is the same selective judgment that makes highlighting useful when it is done sparingly. The margin also anchors the note to its exact context, which a separate notebook loses.
Digital annotation extends the margin beyond the physical page: highlights and notes on web pages, PDFs, and ebooks are marginalia that can be searched, shared, and revisited. The social dimension Jackson documents, readers reading each other's reading, is exactly what social highlighting platforms recreate online.