Book Summary & Highlights: How To Take Smart Notes



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The key to good and efficient writing lies in the intelligent organisation of ideas and notes. This book helps students, academics and nonfiction writers to get more done, write intelligent texts and learn for the long run. It teaches you how to take smart notes and ensure they bring you and your projects forward. The Take Smart Notes principle is based on established psychological insight and draws from a tried and tested note-taking-technique. This is the first comprehensive guide and description of this system in English, and not only does it explain how it works, but also why. It suits students and academics in the social sciences and humanities, nonfiction writers and others who are in the business of reading, thinking and writing. Instead of wasting your time searching for notes, quotes or references, you can focus on what really counts: thinking, understanding and developing new ideas in writing. It does not matter if you prefer taking notes with pen and paper or on a computer, be it Windows, Mac or Linux. And you can start right away.

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How To Take Smart Notes: 10 Principles to Revolutionize Your Note-Taking and Writing

Iklas 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.


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:

  • Luhmann wrote down interesting or potentially useful ideas he encountered in his reading on uniformly sized index cards
  • He wrote only on one side of each card to eliminate the need to flip them over, and he limited himself to one idea per card so they could be referenced individually
  • Each new index card received a sequential number, starting at 1. When a new source was added to that topic, or he found something to supplement it, he would add new index cards with letters as suffixes (1a, 1b, 1c, etc.)
  • These branching connections were marked in red as close as possible to the point where the branch began
  • Any of these branches could also have their own branches. The card for fellow German sociologist Jürgen Habermas, for example, was labeled 21/3d26g53
  • As he read, he would create new cards, update or add comments to existing ones, create new branches from existing cards, and create new links between cards on different “strands”

This diagram shows how subtopics branched off from main topics:


A diagram showing Luhmann’s system, with new cards branching off from existing ones and receiving a letter designation [Source:

Zettelkasten Blog

]Not only did this create a system that could extend infinitely in any direction, but it also gave each index card a permanent ID number. This number could be referenced from any other card, because it would never change. The branches created “strands” of thought that one could enter at any point, following it downstream to be elaborated upon or upstream to its source.

It also led to a meaningful topography within the system: Topics that had been extensively explored had long reference numbers, making their length informative on its own. There is no hierarchy in the zettelkasten, which means it can grow internally without any preconceived scheme. By creating notes as a decentralized network instead of a hierarchical tree, Luhmann anticipated hypertext and URLs.

Over his 30-year career, Luhmann published 58 books and hundreds of articles on the way to completing his two-volume masterwork, The Society of Society (1997). It presented a radical new theory that not only changed sociology but also provoked heated discussions in philosophy, education, political theory, and psychology.

For years, the importance of Luhmann’s slip-box was underestimated. As early as 1985, he would regularly point to it as the source of his amazing productivity: “I, of course, do not think everything by myself. It happens mainly within the slip-box” (Luhmann, Baecker, and Stanitzek 1987, 142). Until recently, no one believed that such a simple system could produce such prolific output. We are so used to the idea that great outcomes require great (and complicated) efforts.

But Luhmann often remarked that he never forced himself to do anything he didn’t feel like doing: “I only do what is easy. I only write when I immediately know how to do it. If I falter for a moment, I put the matter aside and do something else” (Luhmann et al., 1987, 154f).

Wouldn’t it make sense that such output over so many years would be possible because it was simple and easy, not in spite of it? Upon his death, Luhmann’s slip-box contained 90,000 notes. This may seem like a staggering number until you realize that it amounts to only six notes per day.

Let’s look deeper at the main principles that Luhmann used in his work, which Ahrens has adapted to the modern age. The explosion of technology and connectivity has inundated us with an overabundance of information. These principles go a long way toward reestablishing the boundaries and constraints that creativity needs to thrive.

Big Ideas

Atomic Notes

Instead of adding notes to existing categories or the respective texts, he wrote them all on small pieces of paper, put a number in the corner and collected them in one place: the slip-box.

Slipbox Method

#1: Bibliographical

Contained the references and brief notes on the content of the literature.
Whenever he read something, he would write the bibliographic information on one side of a card and make brief notes about the content on the other side (Schmidt 2013, 170). These notes would end up in the bibliographic slip-box.

#2: Main one

Where he collected and generated his ideas, mainly in response to what he read. The notes were written on index cards and stored in wooden boxes.
In a second step, shortly after, he would look at his brief notes and think about their relevance for his own thinking and writing. He then would turn to the main slip-box and write his ideas, comments and thoughts on new pieces of paper, using only one for each idea and restricting himself to one side of the paper, to make it easier to read them later without having to take them out of the box. He kept them usually brief enough to make one idea fit on a single sheet, but would sometimes add another note to extend a thought.
Luhmann’s slip-box contains about 90,000 notes, which sounds like an incredibly large number. But it only means that he wrote six notes a day from the day he started to work with his slip-box until he died.

He usually wrote his notes with an eye towards already existing notes in the slip-box. And while the notes on the literature were brief, he wrote them with great care, not much different from his style in the final manuscript: in full sentences and with explicit references to the literature from which he drew his material. More often than not, a new note would directly follow up on another note and would become part of a longer chain of notes. He then would add references to notes somewhere else in the slip-box, some of them which were located nearby, others in completely different areas and contexts. Some were directly related and read more like comments, others contained not-so-obvious connections. Rarely would a note stay in isolation.

Organization Method


The trick is that he did not organise his notes by topic, but in the rather abstract way of giving them fixed numbers. The numbers bore no meaning and were only there to identify each note permanently. If a new note was relevant or directly referred to an already existing note, such as a comment, correction or addition, he added it directly behind the previous note. If the existing note had the number 22, the new note would become note number 23. If 23 already existed, he named the new note 22a. By alternating numbers and letters, with some slashes and commas in between, he was able to branch out into as many strings of thought as he liked. For example, a note about causality and systems theory carried the number 21/3d7a7 following a note with the number 21/3d7a6.
Luhmann, working with pen and paper, would put a note behind an existing one and number it accordingly. If the existing note bore the number 21, he numbered the new note 22. If note number 22 already existed, he would still add it behind 21, but number it 21a. By alternating numbers and letters, he was able to branch out into an infinite number of sequences and sub-sequences internally with no hierarchical order.
These note sequences are the backbone of text development. They combine the advantages of an abstract with a topic-related order. A pure topic-related order would have to be organised top down and requires a hierarchical order up front. A pure abstract order would not allow idea clusters and topics to be built bottom up. The individual notes would stay mostly independent and isolated with only one-dimensional references – pretty much like a one-person Wikipedia stripped of the knowledge and fact-checking abilities of the community. But a loose order of sequences allows freedom to change course when necessary and provides enough structure to build up complexity.
The note sequences are the clusters where order emerges from complexity. We extract information from different linear sources and mix it all up and shake it until new patterns emerge. Then, we form these patterns into new linear texts.

Ahrens, Sönke. How to Take Smart Notes: One Simple Technique to Boost Writing, Learning and Thinking – for Students, Academics and Nonfiction Book Writers (pp. 108-109). UNKNOWN. Kindle Edition.



These links can help us to find surprising connections and similarities between seemingly unrelated topics. Patterns might not become visible right away, but they might emerge after multiple note-to-note links between two topics have been established. It is no coincidence that one of the main features of Luhmann’s theory of social systems is its discovery of structural patterns that could be found in very different parts of society. For example, he was able to show how vastly different things like money, power, love, truth and justice can be seen as social inventions that solve structurally similar problems (they all can be seen as media that make the acceptance of certain communication offers more likely, cf. Luhmann 1997, chapter 9–12). Observations like these could never be done nor explained by someone who is working with a system that keeps things neatly separated by preconceived themes and topics. The search for meaningful connections is a crucial part of the thinking process towards the finished manuscript. But here, it is dealt with in a very concrete way. Instead of figuratively searching our internal memory, we literally go through the file-box and look for connections. By dealing with actual notes, we are also less prone to imagine connections where there aren’t any, as we can see in black and white if something makes sense or not. As we are making these connections, we build up an internal structure of the slip-box, which is shaped by our thinking. While this structure builds up externally and independently of our limited memory, it will, in return, shape our thinking as well and help us to think in a more structured way. Our ideas will be rooted in a network of facts, thought-through ideas and verifiable references. The slip-box is like a well-informed but down-to-earth communication partner who keeps us grounded. If we try to feed it some lofty ideas, it will force us to check first: What is the reference? How does that connect to the facts and the ideas you already have?


Whenever he added a note, he checked his slip-box for other relevant notes to make possible connections between them. Adding a note directly behind another note is only one way of doing this. Another way is by adding a link on this and/or the other note, which could be anywhere in the system.
By adding these links between notes, Luhmann was able to add the same note to different contexts.
What does help for true, useful learning is to connect a piece of information to as many meaningful contexts as possible, which is what we do when we connect our notes in the slip-box with other notes. Making these connections deliberately means building up a self-supporting network of interconnected ideas and facts that work reciprocally as cues for each other.
Ideally, new notes are written with explicit reference to already existing notes.
The references between the notes are much more important than the references from the index to a single note.
Luhmann used four basic types of cross-references in his file-box (Schmidt 2013, 173f; Schmidt 2015, 165f). Only the first and last are relevant for the digital Zettelkasten, the other two are merely compensating for restrictions of the analogue pen and paper version. You don’t need to concern yourself with them if you use the digital program. 1.  The first type of links are those on notes that are giving you the overview of a topic. These are notes directly referred to from the index and usually used as an entry point into a topic that has already developed to such a degree that an overview is needed or at least becomes helpful. On a note like this, you can collect links to other relevant notes to this topic or question, preferably with a short indication of what to find on these notes (one or two words or a short sentence is sufficient). This kind of note helps to structure thoughts and can be seen as an in-between step towards the development of a manuscript. Above all, they help orientate oneself within the slip-box. You will know when you need to write one. Luhmann collected up to 25 links to other notes on these kind of entry notes. They don’t have to be written in one go as links can be added over time, which again shows how topics can grow organically. What we think is relevant for a topic and what is not depends on our current understanding and should be taken quite seriously: It defines an idea as much as the facts it is based on. What we regard as being relevant for a topic and how we structure it will change over time. This change might lead to another note with a different, more adequate topic structure, which then can be seen as a comment on the previous note. Thankfully, it won’t make all the other notes redundant. As mentioned before: All we have to do is to change the entry in the index to this new note and/or indicate on the old note that we now consider a new structure more fitting. 2.  A similar though less crucial kind of link collection is on those notes that give an overview of a local, physical cluster of the slip-box. This is only necessary if you work with pen and paper like Luhmann. While the first type of note gives an overview of a topic, regardless of where the notes are located within the slip-box, this type of note is a pragmatic way of keeping track of all the different topics discussed on the notes that are physically close together. As Luhmann put notes between notes to internally branch out subtopics and sub-subtopics, original lines of thoughts were often interrupted by hundreds of different notes. This second type of note keeps track of the original lines of thought. Obviously, we don’t need to worry about this if we work with the digital version. 3.  Equally less relevant for the digital version are those links that indicate the note to which the current note is a follow-up and those links that indicate the note that follows on the current note. Again, this is only relevant to see which notes follow each other, even if they don’t physically stand behind each other anymore. The digital Zettelkasten automatically adds these kinds of backlinks and presents you the relevant notes in a note sequence. 4.  The most common form of reference is plain note-to-note links. They have no function other than indicating a relevant connection between two individual notes. By linking two related notes regardless of where they are within the slip-box or within different contexts, surprising new lines of thought can be established. These note-to-note links are like the “weak links” (Granovetter 1973) of social relationships we have with acquaintances: even though they are usually not the ones we turn to first, they often can offer new and different perspectives.


Keywords should always be assigned with an eye towards the topics you are working on or interested in, never by looking at the note in isolation.
This is also why this process cannot be automated or delegated to a machine or program – it requires thinking.
Good keywords are usually not already mentioned as words in the note. Assume I have the note “A sudden increase of ad-hoc theories is for Kuhn a sign that a normal-science phase might be in crisis (Kuhn 1967, 96).” A fitting keyword might be “paradigm change,” but that phrase is not in the note and therefore would not be suggested by the program. Assigning keywords is much more than just a bureaucratic act. It is a crucial part of the thinking process, which often leads to a deeper elaboration of the note itself and the connection to other notes.


The last element in his file system was an index, from which he would refer to one or two notes that would serve as a kind of entry point into a line of thought or topic. Notes with a sorted collection of links are, of course, good entry points.

Benefits Of The Method

Detect Errors In Our Thinking

Comparing notes also helps us to detect contradictions, paradoxes or oppositions – important facilitators for insight. When we realise that we used to accept two contradicting ideas as equally true, we know that we have a problem – and problems are good because we now have something to solve.

Counteract Availability Bias

Feature-positive effect (Allison and Messick 1988; Newman, Wolff, and Hearst 1980; Sainsbury 1971). This is the phenomenon in which we tend to overstate the importance of information that is (mentally) easily available to us and tilts our thinking towards the most recently acquired facts, not necessarily the most relevant ones. Without external help, we would not only take exclusively into account what we know, but what is on top of our heads.[35] The slip-box constantly reminds us of information we have long forgotten and wouldn’t remember otherwise – so much so, we wouldn’t even look for it.

Compound Interest

Putting notes into the slip-box, however, is like investing and reaping the rewards of compounded interest (which would in this example almost pay for the whole flat).
And likewise, the sum of the slip-box content is worth much more than the sum of the notes. More notes mean more possible connections, more ideas, more synergy between different projects and therefore a much higher degree of productivity.

Explanation Effect

Taking permanent notes of our own thoughts is a form of self-testing as well: do they still make sense in writing? Are we even able to get the thought on paper? Do we have the references, facts and supporting sources at hand? And at the same time, writing it is the best way to get our thoughts in order. Writing here, too, is not copying, but translating (from one context and from one medium into another). No written piece is ever a copy of a thought in our mind.
Any thought of a certain complexity requires writing. Coherent arguments require the language to be fixed, and only if something is written down is it fixed enough to be discussed independently from the author. The brain alone is too eager to make us feel good – even if it is by politely ignoring inconsistencies in our thinking. Only in the written form can an argument be looked at with a certain distance – literally. We need this distance to think about an argument – otherwise the argument itself would occupy the very mental resources we need for scrutinizing it.
Luhmann states as clearly as possible: it is not possible to think systematically without writing (Luhmann 1992, 53).
Almost all agree nowadays that real thinking requires some kind of externalization, especially in the form of writing. “Notes on paper, or on a computer screen [...] do not make contemporary physics or other kinds of intellectual endeavour easier, they make it possible” is one of the key takeaways in a contemporary handbook of neuroscientists (Levy 2011, 290) Concluding the discussions in this book, Levy writes: “In any case, no matter how internal processes are implemented, insofar as thinkers are genuinely concerned with what enables human beings to perform the spectacular intellectual feats exhibited in science and other areas of systematic enquiry, as well as in the arts, they need to understand the extent to which the mind is reliant upon external scaffolding.”


Deciding What To Memorize

“Selection is the very keel on which our mental ship is built. And in this case of memory its utility is obvious. If we remembered everything, we should on most occasions be as ill off as if we remembered nothing. It would take as long for us to recall a space of time as it took the original time to elapse, and we should never get ahead with our thinking.” (William James 1890, 680).

Retrieval Strength

Learning would be not so much about saving information, like on a hard disk, but about building connections and bridges between pieces of information to circumvent the inhibition mechanism in the right moment. It is about making sure that the right “cues” trigger the right memory, about how we can think strategically to remember the most useful information when we need it.

Case Studies

Solomon Shereshevsky: The Person Who Never Forgot

To be able to remember everything and not having to resort to any external memory sounds great initially. But you might think differently if you are familiar with the story of a man who was really able to remember almost everything. The reporter Solomon Shereshevsky (Lurija 1987) is one of the most famous figures in the history of psychology. When his supervisor saw that he didn’t take any notes during their meetings, he first doubted Shereshevsky’s dedication to the job, but shortly after, it was rather his own sanity that he doubted. When he confronted Shereshevsky with what seemed to him like lazy behaviour, Shereshevsky started to recount every single word that was spoken during the meeting and continued to recount verbatim all the meetings they had ever had. His colleagues were astonished, but the person most astonished was Shereshevsky himself. It was the first time he realised that everyone else seemed to have forgotten almost everything. Even those who had taken notes couldn’t remember even a fraction of what seemed normal for him. Aleksandr Romanovich Luria, the psychologist who subsequently tested him in all conceivable ways, couldn’t find any of the usual restrictions people normally have in their memories. But it also became clear that this advantage came at a huge cost: It wasn’t just that Shereshevsky was able to remember so much, he had trouble forgetting anything. The important things got lost under a pile of irrelevant details that involuntarily came to his mind. Although he was very good at remembering facts, Shereshevsky was almost incapable of getting the gist of something, the concepts behind the particulars and distinguishing the relevant facts from minor details. He had great trouble relating to literature or poetry. He could repeat a novel word by word, but the greater meaning would be lost on him. While Romeo and Juliet is for most of us a story of love and tragedy, for him it would be the story of “Two households, both alike in dignity, In fair Verona where we lay our scene, From ancient grudge break to new mutiny, Where civil blood makes civil hands unclean...” It should be obvious that for academic thinking and writing, the gift of being able to remember everything is a serious liability.

Niklas Luhmann

In 30 years, he published 58 books and hundreds of articles, translations not included.
He not only stressed that he never forced himself to do something he didn’t feel like, he even said: “I only do what is easy. I only write when I immediately know how to do it. If I falter for a moment, I put the matter aside and do something else.” (Luhmann et al., 1987, 154f.)[4]

Anthony Trollope

The technique of writing a certain amount every day was perfected by Anthony Trollope, one of the most popular and productive authors of the 19th century: He would start every morning at 5:30 a.m. with a cup of coffee and a clock in front of him. Then he would write at least 250 words every 15 minutes. This, he writes in his autobiography: “allowed me to produce over ten pages of an ordinary novel volume a day, and if kept up through ten months, would have given as its results three novels of three volumes each in the year” (Trollope, 2008, 272). And that, mind you, was before breakfast.

Richard Feynman

Most people still think about thinking as a purely internal process, and believe that the only function of the pen is to put finished thoughts on paper. Richard Feynman once had a visitor in his office, a historian who wanted to interview him. When he spotted Feynman’s notebooks, he said how delighted he was to see such “wonderful records of Feynman’s thinking.” “No, no!” Feynman protested. “They aren’t a record of my thinking process. They are my thinking process. I actually did the work on the paper.” “Well,” the historian said, “the work was done in your head, but the record of it is still here.” “No, it’s not a record, not really. It’s working. You have to work on paper, and this is the paper.”[33] Source: “Genius: The Life And Science of Richard Feynman,” James Gleick, Pantheon Books, 1992 (see pg. 409).


Part 1: Every


Michael Highlights

Notes are only as valuable as the note and reference networks they are embedded in.

Most Popular Highlights From Kindle Users

Studies on highly successful people have proven again and again that success is not the result of strong willpower and the ability to overcome resistance, but rather the result of smart working environments that avoid resistance in the first place (cf. Neal et al. 2012; Painter et al. 2002; Hearn et al. 1998). Instead of struggling with adverse dynamics, highly productive people deflect resistance, very much like judo champions. This is not just about having the right mindset, it is also about having the right workflow. It

The Slip-Box Manual

Whenever he read something, he would write the bibliographic information on one side of a card and make brief notes about the content on the other side (Schmidt 2013, 170). These notes would end up in the bibliographic slip-box.
He did not just copy ideas or quotes from the texts he read, but made a transition from one context to another.
The trick is that he did not organise his notes by topic, but in the rather abstract way of giving them fixed numbers.
In the old system, the question is: Under which topic do I store this note? In the new system, the question is: In which context will I want to stumble upon it again?
The slip-box is designed to present you with ideas you have already forgotten, allowing your brain to focus on thinking instead of remembering.


Writing is, without dispute, the best facilitator for thinking, reading, learning, understanding and generating ideas we have.


It is important to reflect on the purpose of these different types of notes. Fleeting notes are there for capturing ideas quickly while you are busy doing something else. When you are in a conversation, listening to a lecture, hear something noteworthy or an idea pops into your mind while you are running errands, a quick note is the best you can do without interrupting what you are in the middle of doing. That might even apply to reading, if you want to focus on a text without interrupting your reading flow. Then you might want to just underline sentences or write short comments in the margins. It is important to understand, though, that underlining sentences or writing comments in the margins are also just fleeting notes and do nothing to elaborate on a text. They will very soon become completely useless – unless you do something with them. If you already know that you will not go back to them, don’t take these kind of notes in the first place. Take proper notes instead. Fleeting notes are only useful if you review them within a day or so and turn them into proper notes you can use later. Fleeting literature notes can make sense if you need an extra step to understand or grasp an idea, but they will not help you in the later stages of the writing process, as no underlined sentence will ever present itself when you need it in the development of an argument. These kinds of notes are just reminders of a thought, which you haven’t had the time to elaborate on yet. Permanent notes, on the other hand, are written in a way that can still be understood even when you have forgotten the context they are taken from.
Keywords should always be assigned with an eye towards the topics you are working on or interested in, never by looking at the note in isolation. Assigning keywords is much more than just a bureaucratic act. It is a crucial part of the thinking process, which often leads to a deeper elaboration of the note itself and the connection to other notes.

Most Popular Highlights From Goodreads Users

Learning, thinking, and writing should not be about accumulating knowledge, but about becoming a different person with a different way of thinking. This is done by questioning one’s own thinking routines in light of new experiences and facts.”

Quotes In The Book

“Every note is just an element in the network of references and back references in the system, from which it gains its quality.” (Luhmann 1992)
By learning, retaining, and building on the retained basics, we are creating a rich web of associated information. The more we know, the more information (hooks) we have to connect new information to, the easier we can form long-term memories. […] Learning becomes fun. We have entered a virtuous circle of learning, and it seems as if our long-term memory capacity and speed are actually growing. On the other hand, if we fail to retain what we have learned, for example, by not using effective strategies, it becomes increasingly difficult to learn information that builds on earlier learning. More and more knowledge gaps become apparent. Since we can’t really connect new information to gaps, learning becomes an uphill battle that exhausts us and takes the fun out of learning. It seems as if we have reached the capacity limit of our brain and memory. Welcome to a vicious circle. Certainly, you would much rather be in a virtuous learning circle, so to remember what you have learned, you need to build effective long-term memory structures. (Helmut D. Sachs 2013, 26)

To Research Further

Albert Rothenberg suggests that the construction of oppositions is the most reliable way of generating new ideas (Rothenberg 1971; 1996; 2015).