My annotation system has evolved considerably over twelve years of serious reading. Current state: pencil for everything in books I own, nothing in library books. I use the margins for two kinds of marks — a vertical line for passages worth returning to, and written notes for anything requiring a response. I keep a reading notebook alongside the book for longer thoughts that don't fit in margins.

I've tried digital annotation systems. Kindle highlights are useful for searchability but they don't produce the physical engagement with text that pencil does. There's something about writing in a margin that seems to fix the thought in memory in a way typing doesn't. I suspect this is idiosyncratic but several annotating friends report the same thing.

The best thing that happens with heavy annotation is rereading. When I returned to my annotated copy of Blood Meridian after eight years, I was having a conversation with my past self about the same text. That's not something a clean copy could offer.