I long ago stopped reading books on note-taking. They were always too vague and boring, full of platitudes that had little to do with the world outside academia. I especially avoided “how-to” style books on the subject.

They would often list dozens of tips and tricks that had little to do with each other. There was never an overarching system for turning notes into concrete results.

But recently I picked up How To Take Smart Notes by Sönke Ahrens. Ahrens is a Lecturer in Philosophy of Education at the University of Duisburg-Essen and also coaches students, academics, and professionals with a focus on time management, decision-making, and personal growth.

It is by far the most impactful and profound book I’ve ever read on the subject. I was astounded to encounter in its pages (with uncanny similarity) many of the same principles I had discovered over 10 years of personal experience.

This book is so full of insights that it broke my usual approach to summarizing books.

My approach is based on the assumption that most books are a few morsels of real insight wrapped in layers and layers of fluff. As I read, I systematically unravel those layers of fluff and extract only those insights, like a chemist distilling only the purest compound.

But this book is not written in the usual way. It is written using an external thinking system, which I call a Second Brain.

The evidence is clear: Instead of squeezing as many pages as possible out of one idea, How To Take Smart Notes squeezes as many ideas as possible onto every page. Every paragraph has a point, and I struggled to leave anything out of this summary.

By identifying the principles that stand the test of time despite huge changes in the underlying technology, we can better understand the essential nature of the creative process. We can focus our efforts on mastering the art of creative note-taking, producing more insightful writing, and fulfilling our full potential.

What the book is about

How To Take Smart Notes is a book on note-taking for students, academics, and non-fiction writers.

It promises to help readers adopt “a reliable and simple external structure to think in that compensates for the limitations of our brains.” By adopting such a system, Ahrens promises that we will be able to “efficiently turn our thoughts and discoveries into convincing written pieces and build up a treasure of smart and interconnected notes along the way.”

While producing published written works is the end goal, is it not the only goal. Ahrens argues convincingly that turning one’s thoughts into writing isn’t just useful for writers but for anyone who wants to improve their thinking and learning in general.

By focusing on writing, Ahrens is able to speak in concrete terms about a specific creative process while simultaneously drawing universal conclusions. Instead of notes becoming a “graveyard for thoughts,” they can become a life-long pool of rich and interconnected ideas we can draw on no matter where our interests lead us.

Luhmann’s slip-box

Ahrens’ approach to note-taking was inspired by the 20th-century German sociologist Niklas Luhmann (1927-1998). Luhmann was a prolific note-taker, writer, and academic. Early in his academic career, Luhmann realized that a note was only as valuable as its context – its network of associations, relationships, and connections to other information. 

Niklas Luhmann
He developed a simple system based on paper index cards, which he called his “slip-box” (or zettelkasten in German). It was designed to connect any given note to as many different potentially relevant contexts as possible. 

Luhmann rejected alphabetical categorization of his notes, along with fixed categories like the Dewey Decimal System. He intended his notes not just for a single project or book but for a lifetime of reading and researching. He designed his slip-box as a research database made up of index cards (zettel) that were “thematically unlimited” and could be infinitely extended in any direction.
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One of the 90,000 index cards Luhmann created over his 30-year career, on Gleichheit (“equality”). Note the red number in the bottom-left corner indicating a branching topic. You can view a full archive of Luhmann’s notes in an online database maintained by the University of Bielefeld. [Source: Marvin Blum]
Although it appeared to be just a simple filing system made up of index cards, Luhmann’s slip-box grew to become an equal thinking partner in his work. He described his system as his secondary memory (zweitgedächtnis), alter ego, or reading memory (lesegedächtnis). He reported that it continuously surprised him with ideas he’d forgotten he had. Because of this, he claimed that there was actual communication going on between himself and his zettelkasten. As he built up his collection of notes, he embarked on a series of achievements that would eventually make him one of the most influential sociologists and scientists of the 20th century. 

A picture of the very first notecard Luhmann added to his slip-box, labeled with a number 1 in the top-left corner. It begins “1 Introduction; It must be attempted to explain the criteria and concepts as clearly as is possible so that their inadequacy and imperfection becomes clear.” [Source: Taking Note blog]
Here’s how it worked: