I like the reminder that this is a thing and it can/should be done. I grew up reading my dad's leftover WWII non-fiction, in which he typically corrected the a

I like the reminder that this is a thing and it can/should be done. I grew up reading my dad's leftover WWII non-fiction, in which he typically corrected the authors with little gems like "NO!!! A6M2 Zero used 20mm cannon and .303, NOT .50 cal. SLOPPY." Since then I've realized that these scribblings can be useful for a variety of things, like: - Things to remember for later: "Amazing quote." Then it's very easy to thumb through and find that stuff later. For large tomes like scripture it can help to use expanded notation schemes, like highlighters of various colors, symbols representing topics, and so on. If you stick with "amazing quote" while reading the NT or the Quran or something else for the first time, you will quickly get lost when trying to find that one quote. - Frustrations, as above: "WHY is the author writing like this? This entire chapter is fluff!" - Questions: "Who could have committed this crime???" Sometimes just getting the information out of one's own head allows the question to settle in, or to be reviewed and not forgotten later. - Things to research. I use a little icon like ->O for that, indicating directional attention toward an object. For example, the book refers to another book, or a website, and I want to follow up and learn about it. - Building a mental model / framework in order to leverage what the book is saying: "This is step 1 of the author's model for identifying tropospheric propagation conditions, and step 2 seems to be given on page 42." Going beyond marginalia, I have also kept lots of book logs, where I reference a page number and date and get my thoughts onto paper as I read. A log format has its downsides, one of which is that it does not lend itself easily to the expression and design of formal mental models _in one place_. So I usually combine a log format with some other kind of presentational area in my notes that is meant to unify and refine my concept of what can be leveraged, and by which method(s). Reviewing this before I press "add comment," I realize why I like paper books so much...but I guess with e-books you can still keep a separate paper log. Anyway thanks for posting!