Active Reading and Annotation

Reading without notes is leaking water. The book passes through you — interesting in the moment, forgotten in weeks. Months later you remember only that you read it, maybe that you liked it. The specific ideas, the formulations, the connections to other thoughts — gone.

Annotation is the practice of making reading stick. Not by remembering more, but by processing more deeply in the first moment. The marks in the margin are evidence of engagement. The notes extracted afterward are the residue of thought.

Marginalia — notes in the margin — is the oldest annotation technology. Mortimer Adler, author of How to Read a Book, described the practice:

Underlining or highlighting: Mark key passages. Limit to truly important sentences or you’ll highlight everything.

Vertical lines in margin: For passages too long to underline. Bracket the section.

Stars or asterisks: Reserve for the ten to twenty most important points in the book. These are what you’ll return to.

Numbers in margin: For sequences — steps in an argument, related points across pages.

References in margin: “cf. p. 94” or “compare with tacit knowledge.” Connect the current passage to other thoughts.

Circled key terms or phrases: Identify the concepts doing heavy lifting.

Notes in top/bottom margin or end pages: Responses, questions, summaries, page number indices for key themes.

The system matters less than consistency. Pick conventions and stick with them. The marked-up book becomes a conversation with your past self.

Most highlighting is useless. The fluorescent line across a sentence feels like engagement but produces nothing. The sentence is marked, not processed. Passive highlighting creates the illusion of learning while sidestepping the work of learning.

Useful highlighting is selective and purposeful:

Limit highlighting to what you’d quote or teach. If you wouldn’t cite it, don’t mark it.
Add margin notes explaining why you marked it. The note forces processing.
Review highlights within days. The mark should trigger recall; if it doesn’t, the marking was too passive.

Austin Kleon’s rule: “Don’t read with a highlighter. Read with a pen.” Writing — even brief margin notes — engages differently than marking.

The extraction problem: how do notes in books become notes in your system? A book full of marginalia is useful for rereading that book. But ideas work best when they connect across books.

Approaches vary:

Progressive summarization (Tiago Forte): Highlight in the book, then highlight your highlights, then highlight those highlights. Each pass compresses. The final residue enters your notes.

Literature notes (Zettelkasten): After finishing a chapter or book, write brief notes in your own words. One note per important idea. Link these to permanent notes in your system.

Kindle/Readwise export: Digital highlights extract automatically. Review and expand in a processing session. The friction is lower; the danger is accumulating highlights without processing.

The transfer matters because ideas connect across sources. The insight from book A relates to the question in book B. You won’t notice the connection unless both ideas live somewhere you can see them together.

Physical versus digital annotation involves tradeoffs:

Physical books: Higher friction in capture, but kinesthetic engagement (the feel of pen on page) may deepen processing. Marginalia stays with the book; extraction requires a second pass. Works well for dense, rereadable texts.

Digital reading (Kindle, PDF): Lower friction in capture, easy export, searchable. But the ease of highlighting enables passive marking. Works well for information-dense reading where you need the ideas but won’t reread the source.

Audiobooks and podcasts: Capture is hardest. Most listeners bookmark and never return. Voice notes or stopping to dictate work but break flow.

Some people print PDFs to annotate by hand, then scan or transcribe. The friction is intentional — it forces selectivity.

Reading isn’t complete until the notes exist. The book was the input; the notes are the output. Without notes, reading is consumption. With notes, reading is production.

The goal isn’t to remember everything. It’s to retain the specific ideas worth keeping, in forms you can use.

Go Deeper

Books

How to Read a Book by Mortimer Adler — The classic on active reading. Chapter on marking books is essential.
How to Take Smart Notes by Sönke Ahrens — Zettelkasten approach including literature note technique.

Essays

Austin Kleon’s posts on marginalia — Visual examples and philosophy of marking books.
Ryan Holiday’s notecard system — Index card approach to extracting and organizing ideas.