Zettelkasten
Everything You Need to Know
No matter how poorly we take notes, we never receive immediate negative feedback. That’s why we fail to appreciate the importance of note-taking. (The Toothbrushing Paradox)
People hold a deep-rooted belief that notes must start from a blank page. But in truth, that is not the case. Great writing comes from a great system.
To achieve excellent results, you need a system that does the work — and you need to be sufficiently skilled in that system. A flute is capable of producing beautiful sound. Yet no one can produce beautiful sound on a flute from the very beginning. “Outstanding performance comes from (1) outstanding tools and (2) a deep understanding of how to use them.”
Bad routines control people and prevent them from moving in a positive direction. Good routines allow people to maintain focus and enter a state of flow. The state of flow is not accidental.
Writing requires new ideas, and new ideas do not come from planning.
The more books you read, the more you discover that ideas you thought were your own have already been thought of by someone else. That is why we should focus on the connections between ideas.
Those who aren’t skilled don’t find their work particularly difficult. They simply get through it without much trouble. Those who are skilled, on the other hand, hold themselves to extremely high standards. The difficulty of their work is correspondingly high. They may even experience what’s known as impostor syndrome — that feeling of being more than capable, yet convinced they can’t handle the task at hand.
Good Solutions Tend to Be Simple — and Come from Unexpected Places
The best way to solve complex problems is to simplify everything and establish a few fundamental principles.
To create a change in work habits, one must move past the stage of “reverting to the familiar old way of doing things.” Meaningful change can only happen when new practices become mechanized and truly part of one’s work.
The lesson GTD teaches us is that it’s important to gather everything that needs to be handled into one place and process it there. By collecting everything in one place and continuously managing all of it, we gain a sense of control.
The secret to building a successful structure lies in a holistic perspective. When we fail to see the whole picture, we find ourselves preoccupied with neglected parts and feel urgency around tasks that aren’t truly important. We must maintain control.
You can also achieve excellent results by following the work process.
The work system must be flexible enough to accommodate all changes in one’s work environment and work rhythm. Strong willpower is certainly necessary, but if you can create a smart work environment from the outset, you can achieve outstanding results. Highly productive people do not fight against their given environment — instead, they turn resistance to their advantage.
2. Everything You Need to Do
Let’s think about a situation where you need to write something, but all the material is already fully prepared. All you have to do is piece the parts together. Of course, assembling the pieces still requires quite a sophisticated level of thinking — but it’s far better than staring at a blank page, struggling to come up with ideas from scratch.
Moreover, imagine knowing through an index exactly what is missing from the information you have collected. Then you would only need to look further into the parts you don’t know well. Doesn’t that sound wonderful just thinking about it?
For this, it is important to write consistently. And writing is, of course, no easy task. However, writing steadily in ‘my own words’ is a great help in understanding that system. And it is something I have to do anyway (because I need to write!). So let’s keep writing — whether with a pen or a computer.
2.1 Doing Things in Order
1. Write a temporary note
Ideas that suddenly come to mind are jotted down and written in a temporary inbox. There’s no need to write them out too elaborately. They’re simply a means of reminding yourself of the thoughts you had at the time.
2. Writing a Literature Note
I take notes on what I learn while reading. I write down things I especially want to remember or newly discovered ideas. At this point, I should be careful not to copy the text verbatim. Keep it short, and write the content in my own words. The reason for writing in my own words is to make sure I fully understand the meaning.
Generally, when reading, there is no guarantee that only the information you want will be present. It is rare to learn only what you set out to learn. If that were the case, it would mean you already knew the content you were trying to learn, so there would have been no need to study it in the first place. The only way to find out whether an article is useful to you is to read it. That is why you should always read, and take notes on anything that proves helpful. (The non-linearity of learning)
3. Writing Permanent Notes
Review the notes written in [1] and [2], and refine any valid ideas with great precision. At this stage, you must not look at those ideas in isolation — you should also examine the already-completed slip-box alongside them. You need to check whether there are any points that connect to existing notes, and identify what new insights have been gained.
Permanent notes must be written with great precision. Like writing a letter to a friend, they should be written with full context so that anyone can understand them at a glance.
The key is to establish the invariant that everything important lives inside permanent notes.
Permanent notes must be well indexed. The connections between one idea and another must be clearly organized. The purpose of permanent notes is to reach a point where, when the moment of writing arrives, you can write simply by looking at the notes alone — or at least know which topics you still need to explore further. For this reason, it is always necessary to set aside time to verify that the index is accurate.
3. Everything You Need to Have
NASA’s Space Pen and Pencil Story
We must always focus on what matters most. Yet there are far too many techniques that get in the way of that essence. Collecting and adopting various learning methods and note-taking techniques can actually backfire. What we need is not a simpler technique, but a shift in our mental framework. That is what the Zettelkasten method is.
The Zettelkasten method supplements the brain’s weakness in “information storage.”
4. One or Two Things to Keep in Mind
We are exposed to an excessive number of methodologies throughout our lives. We adopt methodologies meant to improve some workflow — things like “How to Get Better at AA” or “How to Get Better at BB” — only to think, “Well, this isn’t really working,” and revert back to the way things were.
The instrument called the flute produces a beautiful sound. However, not everyone can produce a beautiful sound on the flute right away. One must sufficiently master the technique of playing the flute.
To work with similarly excellent work habits, (1) there must be a carefully designed system (= the flute), and (2) the individual must sufficiently master that system (= mastery of how to play the flute).
5. The Only Thing That Matters Is Writing
Generally, we become far more proficient at things when we try to do them ‘deliberately’ well. (Think of the toothbrushing paradox.)
When our primary goal becomes writing notes and connecting them to one another, we will be able to read far more efficiently. We can judge whether a given piece of content is something we need to explore further, something we already know, or something outside our area of research. We can also tell the difference between a merely plausible argument and one genuinely worth remembering. We will read books more diligently and with an active mindset. The same applies to attending seminars. The very way we live will change.
6. The Most Important Thing Is Simplicity
As the volume of notes grows, it is important to have a system that scales its usefulness accordingly.
Simply stacking notes in chronological order causes the cost of finding them to grow exponentially, and you eventually stop looking them up altogether. Notes should be organized so that you can find them immediately based on the context in which you’re searching. This is the purpose of building permanent notes.
Generally, when taking notes, one tends to run into the following questions:
- Something came up that I need to jot down — where do I save it? (-> Zettelkasten: fleeting notes)
- I want to look into something related to a certain topic. What did I look into before? (-> Zettelkasten: permanent notes)
Managing all notes in one place, and organizing them meaningfully based on the context in which you look for them: this is the essence of the Zettelkasten.
The author gives an example of a container system and argues that notes should be written in a standardized format… I didn’t quite understand this part myself.
7. No One Starts from Scratch
All knowledge begins from what has previously been studied. (Hans-Georg Gadamer calls this the “hermeneutic circle.”) This means that in order to conduct any meaningful inquiry, one must examine what has been learned before.
We have long held the belief that writing must always begin from a blank page. We are even told to brainstorm. But starting from a blank page can only ever produce ordinary results. If something outstanding does emerge from a blank page, it is because outstanding research already exists inside one’s head.
But our brains are not that rational, not that logical, and not entirely reliable.
Writing is an inherently nonlinear process. Good material for writing appears in ways that are almost entirely accidental. And as you keep encountering such material, it gradually develops into a single “insight.” Trying to force this nonlinear process into a linear one, however, gets you nowhere. (fictional linearity) Before taking on a writing assignment, you must already have sufficient material in hand — if you don’t, you’re doing the equivalent of a financial advisor explaining retirement savings strategies to a 65-year-old.
(Isn’t programming the same? Don’t we verify “prior knowledge” through interviews, and then expect people to build services within Toss based on that “existing knowledge”?)
8. Go with the Flow
Organizing a slip-box around multiple topics creates that many more feedback loops. Conversely, writing in the conventional way around a single topic traps you within that topic and limits your opportunities for feedback. Why do feedback loops matter? Because the more attempts you make and the less you fear failure, the closer you get to success.
There are two types of mindsets: the “Fixed Mindset” and the “Growth Mindset.” It is generally said that the Growth Mindset has a stronger correlation with success. This is because people with a Growth Mindset are unafraid to try a wider variety of things and continuously improve themselves through feedback. On the other hand, even if someone with a Fixed Mindset starts out highly intelligent and successful, they often end up struggling in the long run because they tend to become consumed by their own current success. The fear of failure can devour them, potentially leaving them paralyzed by a deep-seated fear of failing.
Writing notes allows you to create a meaningful feedback loop. It critically checks whether you have truly read the material. When we read something, we tend to easily assume we understood it. However, taking notes lets you quickly verify whether you genuinely understood something, or whether it contradicts what you already knew. On top of that, periodically reviewing your note box also has the effect of reinforcing what you’ve learned.
The principle of speed reading involves not only reading text faster, but also distinguishing between the important and unimportant parts of a passage — reading the important parts carefully while skimming through the unimportant parts very quickly.
Wikipedia operates on a broadly similar principle, but there is a significant difference from a personal slip-box. Because Wikipedia is written by other people, difficult concepts can suddenly appear without warning. A personal slip-box, however, keeps pace with the individual’s current level of knowledge, so this never happens. (Remember that motivation is closely tied to one’s level of achievement relative to one’s current abilities.)
As we grow older, we find it difficult to learn things that are completely independent of what we already know. On the other hand, it is easier to remember something by connecting it to what we already know. (Isn’t this similar to how even the most absurd mnemonic devices can still help us remember things?)
9. Separating and Connecting
9.1 Fully Focusing on One Task at a Time
We are inherently bad at multitasking. In particular, the amount of time we can maintain focus on any single topic has been shrinking in recent years. In the past, when news segments delivered facts in brief snippets, the narrator’s read would run about 40 seconds. Today it is under 10 seconds. (Sojin Park: The trend of cutting down long YouTube videos into Shorts because they feel too slow could be seen as much the same thing.) It has become far harder for us to practice sustaining our attention.
9.2 Multitasking Is Not a Good Idea
Multitasking diminishes our productivity more than we think. Yet we often fall into the illusion that it actually improves our ability to get things done.
Why do we think that way? There are two main reasons.
First, we lack key quantitative metrics to measure productivity. (Sojin: In the end, isn’t it really about whether you can “trust and delegate” a given task to this person? For example, if someone’s work capability is lacking, you wouldn’t be able to “trust and delegate” a difficult task to them. On the other hand, someone with high work capability is someone you could “trust and delegate” anything to.)
Second, psychology talks about the “mere exposure effect.” The mere exposure effect refers to our tendency to believe that the more we simply “do” something, the better we become at it. (+ There is also a tendency to like it more.)
Moreover, multitasking reduces our efficiency on most tasks. Why is that? There is a limit to how much we can shift our attention. When we keep multitasking, we are constantly forced to redirect our focus. Yet even when we believe we are doing just one thing, we are still continuously shifting our attention. Take writing, for example — it’s not as if we do nothing but type on the keyboard without pause. We think about what sentence should go here, review what we had in mind earlier… Multitasking degrades productivity even in those in-between moments.
This is why we must pay attention to securing a work system that allows us to do ‘one thing’ ‘within a limited time’ ‘without interference from other tasks’.
9.3 Exercising the Right Kind of Attention for the Task
Most things we encounter in life are not all the same. Even when reading, we flip through web novels at a brisk pace. On the other hand, textbooks and other materials that demand an intense level of concentration are read again and again and again. A truly skilled expert can adjust their reading speed and approach to match what the text demands.
For example, concentration isn’t just about maintaining focus on a single task — there is also floating attention, which involves sustaining focus while moving fluidly between various things. When proofreading, for instance, you concentrate on the text itself, whereas when writing, you exercise floating attention in order to think ahead to the next word that will come. Accordingly, we need to adapt the way we direct our attention depending on how we are working.
9.4 Becoming an Expert Rather Than a Master Planner
Unfortunately, most tasks are not that simple. That is why blindly following a manual often leads to a misreading of the current situation. True experts do not follow the manual to the letter. Instead, they make most of their decisions ‘intuitively’, drawing from the accumulated sediment of years of deliberation and learning. Training manuals tell you not to rely on ‘intuition’ but to follow the system — yet the truth is that genuine expertise emerges from intuition.
Experts have already internalized most of the rules and knowledge required for their work, so they have no reason to diligently memorize rules or act strictly by the manual.
9.5 Wrapping Up
Our short-term memory capacity is generally known to hold around seven items. However, by connecting concepts as we memorize them, we can significantly expand that capacity. For example, even when presented with numbers that appear to follow no pattern (1 11 12 1121 122111 …), once you discover the rule, all you need to remember is the rule itself. This is perhaps why we prefer “understanding” over “memorization.” The slip-box system supports this process in a systematic way.
Unfinished tasks are known to continuously encroach on our short-term memory capacity. The GTD system is highly effective in that it “empties” our short-term memory capacity into an external task management system. The same is true of the slip-box. The slip-box augments our short-term memory capacity in that everything we currently know is organized without omission, and we are able to pick up right where we left off whenever we return to our work.
Conversely, if there is something that requires constant deliberation, it is better to keep it in short-term memory capacity. This is because living with it on your mind 24 hours a day, turning it over and over, may bring you the experience of it suddenly resolving in one unexpected moment.
9.6 Reducing Decision Distance
Decision-making itself is yet another resource. A classic example is that CEOs of large companies are known to even standardize their clothing in order to conserve their decision-making resources. Likewise, the act of “deciding” how one will go about performing a task consumes that same resource.
From this perspective, unifying the way we work is very important. Managing notes in the same consistent way will also help conserve decision-making resources.
Also, rest is known to replenish our decision-making resources. Short-term memories are transferred to long-term memory. So let’s make a point of taking intentional breaks throughout the workday. Go for a walk or take a nap!
10.1 Reading to Understand
The notes from a book can be brief or lengthy, depending on the difficulty level of the book being read.
It would also be a good idea to use a bibliographic information system to extract excerpts from literature, so that the content you are reading is not distorted.
If there is no clear reason for taking notes, note-taking will simply be perceived as just another chore.
The primary purpose of taking notes should be set as adding them to permanent notes.
The longer it takes to write a note, the more time you spend thinking about that note — and the deeper your understanding of the lecture content becomes.
10.2 Keeping an Open Mind
People inevitably have confirmation bias and are more receptive to information they believe to be valid. Conversely, they very quickly forget information that could refute their beliefs. For this reason, there is a greater need to take notes on information that has the potential to challenge or disprove what we already believe.
External systems matter only insofar as they help us ultimately achieve what we want. Does the slip-box actually work — does it help us gain insight and produce meaningful writing?
In the linear writing process, we decide on a topic in advance and then gather material around it. This is naturally the moment when confirmation bias takes hold. For this reason, ideas must be developed bottom-up rather than top-down.
Plans for writing are only possible after the discussion has been sufficiently reviewed through the slip-box.
10.3 Grasping the Core
Every piece of writing has a core message and supporting content. And the way each author expresses such content differs. Through note-taking methods, one must learn to quickly identify those various patterns. And the only way to grasp those patterns is simply to keep reading.
10.4 Learning to Read
The less time I spend deeply thinking about an idea, the sooner it slips away from me. Writing that idea down in my own words — however slow the process may be — is the most powerful way to make it take root within me.
Be wary of simply reading a piece of writing over and over again. Repeated reading creates a mere-exposure effect, tricking us into feeling as though we understand the material when we actually do not.
The external system of the slip-box allows us to deliberately test where the boundary lies between what we actually know and what we do not.
10.5 Learning by Reading
Learning is inherently painful. Going to the gym and lifting heavy dumbbells is naturally painful. You can’t just lift light ones, can you? The more effort you put into learning, the longer it stays in your memory.
If you prepare a class so that everything flows smoothly, it increases the likelihood that students will just think “Oh, that’s nice content~” and let it wash over them. It might actually be more effective to deliberately scramble the order so that students react with “Ugh, I guess I’ll just have to look it up myself” — pushing them to study on their own.
The success of learning ultimately depends on how much time we have devoted to studying that concept. If learning is the goal, cramming is an irrational act. (A different story if you’re taking an exam, though!)
The best method of learning is “writing in detail.” It means continuing to think — asking yourself what a sentence means, and why it connects to this or that idea. Of course, if your goal is encyclopedic “shallow and broad knowledge,” this method won’t be effective — but if you’re after genuine, meaningful insight, this approach is well worth it.
Exercise helps us convert what we have learned into long-term memory.
11. Taking Notes Smartly
Information cannot be thought of separately from its context. And it is important to connect what we know to as much context as possible.
11.1 The Path to Success: One Note at a Time
It’s impossible to predict exactly how long it will take to complete a single dissertation. Notes, however, are easy to measure — you can readily track how many you write in a day. Luhmann is said to have left 90,000 notes over the course of his life, which works out to roughly 6 notes per day, sustained continuously.
11.2 Thinking Outside the Brain
Our brains are not particularly rational devices. They tend to settle on a conclusion first, then artificially construct the bridge to get there. That is not something we want to rely on.
By externalizing the thought process through writing, we can compensate for the limitations of the brain. Writing things down prevents us from sneaking in conclusions we’ve already decided on midway through. Every point is written with supporting evidence, and the reasoning process can be verified through the text itself.
Managing a slip box allows you to continuously perform the processes of connecting ideas, reasoning, and drawing conclusions. After reading a book, always add permanent notes and think about what connections can be made with what you already know.
11.3 Learning Without Trying
Our brains evolved to avoid retaining too much information at once. If we had the ability to remember every piece of trivial information, we would be unable to distinguish between what is important and what is not, and we would never have the opportunity to reflect on the true meaning of books, events, and other experiences.
In learning science, “memory ability” is divided into “storage ability” and “connectivity ability.” Storage ability refers to storing fragmentary pieces of information about a given event. Connectivity ability refers to linking that stored information together. And while it has not yet been proven, it is thought that we intentionally suppress our connectivity ability.
Storage capacity is difficult to improve no matter how hard we try. It is said that we already store most information. The problem lies in retrieval ability — the more pathways we have to reach a piece of information, the easier it is to remember. For example, even with lecture content we cannot easily recall, thinking about the “situation in which we learned it” and other associated contexts can sometimes bring that content vaguely to mind. (Sojin: This is similar to asking warm-up questions first during an interview to trigger as much recall as possible.)
Think of mnemonic techniques like the “Memory Palace.” It is a method of memorizing new facts by connecting them to facts you are already “linked” to.
Memorizing isolated facts — “arteries are thick and have no valves; veins are thin and have valves” — is less effective than connecting them to underlying reasoning: “A hose must be strong to withstand pressure, or it will burst” / “The heart beats forcefully, and arteries are the very first vessels to receive that high-pressure blood.”
Trying to memorize many independent facts does not help. What matters is the ability to connect facts, and the more successfully we connect information, the smarter we will become. The Zettelkasten method facilitates this.
12. Developing Ideas
12.1 Developing a Topic
Notes must never stray from the ‘context’ in which I am currently doing research. I need to keep asking myself: why did I become interested in this concept right now, in what kind of situation would I later come back to look it up, and how does it connect to things I have seen before.
From this perspective, the slip-box method cannot be automated.
12.2 Connecting Smartly
How Luhmann Organized His Notes
Niklas Luhmann was a German sociologist who, over his lifetime, produced an extraordinary volume of academic work — more than 70 books and nearly 400 papers. The secret behind this remarkable output was his unique note-taking system: the Zettelkasten (slip box).
What Is a Zettelkasten?
Zettelkasten is German for “slip box” or “card index.” Luhmann wrote his ideas on individual index cards and stored them in a wooden box. What set his system apart was not merely the act of collecting notes, but the way he connected them to one another.
Core Principles of Luhmann’s Method
1. One Idea per Card
Each card contained a single idea or argument. He never crammed multiple concepts onto one card. This made each note an independent, self-contained unit.
2. A Unique Numbering System
Every card was assigned a unique number. When a new idea was related to an existing card, he would branch off from that card’s number. For example:
11a1a11b2
This hierarchical yet flexible numbering allowed the structure to expand endlessly without fixed categories.
3. Linking Notes
The most crucial feature was linking cards to one another. At the bottom of each card, he wrote the numbers of related cards. This created a web of connections rather than a simple linear sequence.
4. An Index
He maintained a separate index card listing keywords alongside the numbers of relevant cards. This served as an entry point into the system, allowing him to navigate it from any starting concept.
How He Used It
Luhmann didn’t treat his Zettelkasten merely as a storage system — he regarded it as a thinking partner. When writing, he would pull out related cards, follow their links, and discover unexpected connections between ideas.
“I never force myself to do anything I don’t feel like doing. I only work on things that are easy for me at the moment.” — Niklas Luhmann
This was possible precisely because the Zettelkasten did the hard organizational work for him. All he had to do was follow the trails of thought already laid out in the box.
Why This Method Works
| Feature | Benefit |
|---|---|
| One idea per card | Easy to reuse and recombine |
| Unique numbering | Grow the system without rigid categories |
| Linking | Surface unexpected connections between ideas |
| Index | Quickly locate any entry point |
Modern Applications
Today, tools like Roam Research, Obsidian, and Notion are inspired by Luhmann’s method. The concept of linking notes with [[wiki-style]] double brackets is a direct digital evolution of his card-linking technique.
The core insight of his method remains just as relevant today:
Don’t organize notes by topic — organize them by connection.
- Overview note: A note that briefly introduces a concept and points to follow-up notes
- Connection note: A note that links to the next note
12.3 Compare, Revise, and Differentiate
We continuously review the slip-box, comparing notes against one another. We look for contradictions, paradoxes, and correlations.
The feature-positive effect for specific items can also be addressed. We tend to make more active use of information that is mentally accessible. In particular, we tend to make more active use of information we have encountered recently. By periodically reviewing notes written long ago through the slip-box, we can compensate for this tendency.
12.4 Assembling the Thinking Toolbox
Storing and recalling fragmented information alone holds little meaning. Only by connecting information does knowledge begin. The Zettelkasten method facilitates this.
Moreover, knowledge stored in the slip-box, much like flashcards, is periodically retrieved. The more we open the slip-box, the better we come to know its contents.
12.5 Using the Slip-Box as a Creativity Machine
Innovation doesn’t appear out of nowhere — it often comes from gradual improvement. And in that process, the connections between concepts play a crucial role. It gives you the ability to see what others cannot.
By writing multiple notes using the Zettelkasten method, you gain the opportunity to compare notes side by side. This makes the similarities and differences between two concepts stand out much more clearly.
We have a natural tendency to compare. True learning happens when we compare.
12.6 Thinking Inside the Box
Through the memo box, two important capabilities can be improved.
First, what truly matters?: The ability to find important connections between notes and to abstract from them
- Investing in stocks means buying a part of a company. Yesterday’s price is not what matters.
Second, lessons from what’s missing: thinking about what’s absent from my notes
- Among British aircraft that returned safely, the survivors show bullet holes concentrated on the wings. According to the distribution, the wings took the most hits, so the armor on the wings should be reinforced. -> But the planes that took hits to the engine crashed without exception…
- Why is money important? What if there were no money? What if I suddenly found myself stranded in an unfamiliar part of America with no dollars?
12.7 Fostering Creativity Within Constraints
Limiting options often increases productivity. By restricting experimental methods, by limiting the medium of exchange (i.e., money), and so on. Creativity can rise by constraining the format and length of notes.
13. Sharing Insights
13.1 From Brainstorming to Box-storming
Brainstorming is dangerous. It causes us to seek out only information related to the topic we initially chose, while preventing us from finding information connected to it in broader ways. (The importance of a proper system) Moreover, as the number of people brainstorming increases, the breadth of ideas tends to narrow and their quality tends to deteriorate.
Turn the effort you put into brainstorming into effort you put into taking notes.
14. Building Habits
What is most relevant to the question of what we will do next is the intention we hold. A strong will — thinking “I should go to the gym!” — is what actually gets us to the gym. Sadly, though, these good intentions rarely last long.
The only willpower that lasts is habit. We generally live lives that are not much different from a week ago, a month ago, or a year ago. This way of living does not change easily. Because of the mere exposure effect, we may even come to believe that the behaviors we are least able to change are the ones most within our power to change.
We are better off finding a new behavior that can replace the habit we want to change, and building that into a habit, rather than trying to change ourselves directly.
Review
A slip-box is like saving for retirement. The earlier you start, the greater the returns that come back to you.
When we’re under stress, it becomes harder to change our behavior. This is sometimes called the tunnel effect. The more stressed we are, the simpler the solutions we think of need to be.