Sönke Ahrens book “How to Take Smart Notes: One Simple Technique to Boost Writing, Learning and Thinking” details the Zettelkasten method, a note-taking system used by sociologist Niklas Luhmann to become incredibly prolific.
Writing notes is an important, in the academic world as much as in everyday life. Having a reliable note-taking system can meaningfully boost productivity and deepen understanding. Reading frequently, as many of us do, demands a method that allows us to grasp the fundamental ideas of a book so that we can return to those notes months or even years later and recover the essence of what we once read.
The core insight is simple: once a good structure is in place, we can trust the system and turn our full attention to what actually matters, namely the content and the ideas we want to develop. A good note-taking solution should be simple enough to start immediately, useful enough to sustain long-term engagement, and modular enough to allow complexity to be added incrementally as our needs grow.
This principle aligns closely with Occam’s razor, the idea that the simplest sufficient solution is almost always the best one. There is no point in building an elaborate system that becomes a burden to maintain; the system should serve the thinking, not the other way around.
The main concept of the method is the slip-box itself, known in German as the Zettelkasten. In its original, physical form, it consisted of two separate boxes of index cards. The first was a bibliographical box, containing references and brief notes about the content of whatever had been read. The second, and more important, was the main slip-box, dedicated to developing and connecting ideas.
The workflow was straightforward. Whenever something was read, a brief bibliographical note would be written, capturing the reference and a short summary of the content. This card would be filed in the bibliographical box, serving as a record of the source material.
The real work, however, happened in a second pass. After some reflection, the reader would revisit those bibliographical notes and consider their relevance to their own thinking and ongoing lines of inquiry. From this reflection, a new note would be written on a fresh card and placed in the main slip-box.
Each card contained one idea and one idea only. These notes were polished and written in complete, considered sentences, as if being composed for an audience. The point was never to blindly copy a quote or transcribe a passage; rather, it was to translate the concept into one’s own words and situate it within the specific context where it might prove useful.
The organization of these notes was itself a form of thinking. Using a system of letters and numbers, cards could be inserted between any two existing notes, creating an effectively infinite space for intermediate ideas within an already established chain of thought. Beyond this sequential ordering, cross-references could be added between cards that were physically distant but intellectually related, creating something remarkably close to what we would today call hyperlinks. A note about a concept in one domain could point directly to a note in an unrelated domain, and it was often in these unexpected connections that the most original insights emerged.
The final element was a simple index, serving as an entry point into particular lines of thought. A handful of index references was enough to walk into the slip-box and follow a thread wherever it led.
That is, in its entirety, the system.
To implement this method today, we need four tools, and the good news is that the entire workflow can be set up with free software.
The first is a capture tool, something to record ideas as they arise. This can be as simple as a piece of paper, a physical scratchpad, or a lightweight digital notes application. This step is purely transient. The capture tool is not the place for detailed thinking; it holds only a quick summary, a reminder, enough to ensure the idea is not lost before it can be properly processed. As a rule of thumb, these fleeting notes should be worked through before the end of the day, so they do not pile up into an unmanageable backlog.
The second tool is a reference manager, whose purpose is to collect and organize the bibliographical information that feeds into our notes. My choice here is Zotero, a free and open-source tool that integrates with most major browsers via a plugin, allowing new references to be captured in a single click while reading online, and it can also be connected directly to the writing environment, making citations seamless when the time comes to write.
The third tool is the slip-box itself. Some people still prefer pen and paper for this, and there is nothing wrong with that approach. The computer can accelerate the creation of links and make formatting more flexible, but the core of the work is not related with software. It is thinking, understanding, and distilling ideas into their most essential form. For those who prefer a digital environment, Zettlr is an excellent free option, built with exactly this kind of note-taking workflow in mind, and it is the tool I use.
The fourth tool is an editor for longer writing, the environment where connected notes eventually become drafts, articles, or more substantial work. In practice, Zettlr covers both the slip-box and the editing function, and its native compatibility with Zotero means that, for most purposes, just these two tools together are sufficient to run the entire system.
Writing is all that matters. When attending a lecture, a conference, a meeting, or reading a book, the objective is to grasp the most important aspects, since it is impossible to write down everything. This constraint makes reading and listening more engaged, because to rephrase concepts in our own words requires that we deeply understand the content we are encountering. In doing so, we are not merely recording information, we are elaborating on its meaning, which in turn makes it far easier to remember in the future. The best way to improve at something is to keep practicing, and if we do that consistently with writing, we will become progressively better writers.
Very often, it is the simplicity of an idea that makes it powerful. Many important discoveries have come from simple ideas, clearly articulated. In note-taking, many people have thought about it and developed systems that made sense to them, such as underlining passages in a book, clipping articles from newspapers, or scribbling in the margins. However, working in this way leaves an inhomogeneous set of notes scattered across different places and formats. When it comes time to write, these people must often brainstorm from scratch, trying to recall and arrange resources that might be relevant to an idea, resources that could be spread across multiple books, folders, or files.
The slip-box inverts this problem. While people in the standard framework ask themselves when it is useful to take a note, with this system the question is simply in which context this idea might be useful again. The slip-box becomes a container of ideas in a standardized format, where all insights are streamlined and ready to be retrieved or published in the future. The more the slip-box grows, the more valuable it becomes, whereas in traditional systems organized by topic, some topics can become too complex or too large and require trimming or reorganization. The slip-box is designed to present ideas in clusters, leaving the brain free to make the connections. It becomes truly useful when it achieves a critical mass, which depends on both the number and the quality of the notes.
There are three types of notes, and distinguishing between them is essential:
Fleeting notes: these are reminders of information, captured quickly and destined to be discarded within a short period, usually a day or two. They exist only to prevent ideas from being lost before they can be properly processed.
Project notes: these are relevant only to a single project. They are kept in a project-specific folder and can be archived upon project completion. They do not belong in the slip-box.
Permanent notes: these will never be thrown away. They contain the necessary information in a standardize, self-contained way, and these are the ones that go into the slip-box.
Separating notes in this way allows us to create a critical mass of ideas within the slip-box, a growing repository of carefully considered thoughts that can be drawn upon indefinitely.
A common mistake is to mix all three types in the same slip-box, diluting good ideas with a mass of notes that are partial, incomplete, or specific to a particular project only. Another mistake is to collect notes only for the sake of a particular project at one time. While this can speed the completion of a specific task, it forces us to start from scratch after each project, and connections with other ideas are never made.
The Zettelkasten has the function of project-specific organization built in, as notes can be easily collected and tagged for a specific project without the risk of interfering with the slip-box’s fundamental purpose. The permanent notes remain in the slip-box, available for reuse and recombination, while project notes serve their temporary purpose and are then set aside.
Many writing methods begin from the premise of “selecting the topic”, then guide the writer through a series of steps to achieve the desired result. The assumption is that people are always starting from a clean sheet, looking for something to write about. In reality, the opposite is more often the case. Most writers have something already, a base of existing knowledge and interest that serves as a foundation for further inquiry. By focusing on what is genuinely interesting and working consistently toward intellectual development, new arguments will emerge naturally from the material collected. From clusters of notes inside the slip-box, possible topics will present themselves, often in ways that could not have been anticipated in advance.
Using the slip-box creates a positive feedback loop. The ability to understand content and express it in one’s own words is important for all writers, but the better we become at that skill, the easier it becomes to take notes, which in turn increases the number of meaningful learning experiences we can have. The more we are able to identify the important parts of a text, the more effective our reading becomes, the more we can read, and the more we can learn. It is a compounding advantage.
Similarly, writing permanent notes creates another virtuous loop. Expressing thoughts in writing makes them deeply our own, and when we try to combine them with other notes, we are forced to check whether there are contradictions or repeated concepts. This process pushes us to clarify, refine, and sometimes revise our thinking.
The slip-box is a map that allows ideas to grow through interconnections. Searching through it will often reveal a set of notes we were not looking for, prompting us to reflect on unexpected connections. The more connected information we have, the more our brain is able to learn and link ideas with each other. This accords with what we know about memory and learning: isolated facts are difficult to retain, but information embedded in a network of meaning is far more durable.
Even if our brain’s ability to learn in isolation likely decreases with age, putting facts into a latticework of mental models, as described here, helps us to learn and connect new information more effectively. Because we are the authors of all the notes, the slip-box is not a dry version of a website or a generic knowledge base. It is linked to the thoughts in our own brain, expressed in our own voice, and it helps us to generate new ideas and develop our theories further. It becomes, over time, an external scaffold for thinking, one that grows more powerful the more it is used.
It is important to focus and concentrate on the writing task. Doing multiple tasks at once, despite some people claiming they are good at it, and the younger generation supposedly even more so, is not good for productivity. Some studies attempt to show the contrary, but they generally fail to compare against a control group and merely measure some kind of output without assessing quality or cognitive cost.
Overall, multitasking decreases efficiency and productivity. This is because multitasking is not truly focusing attention on more than one task at a single time; rather, it is jumping back and forth between two or more tasks, with a consequent drain of energy required to keep refocusing on something different for a short period. The apparent gain arises from the lack of a proper control group, and also from the self-perceived mere-exposure effect: the more we do something, the more we perceive ourselves to be good at it, regardless of objective performance.
Writing something involves more than just typing text. It requires reading, understanding, connecting ideas, structuring sentences, and more, all of which demand a certain degree of sustained attention.
When it comes to attention, there are multiple forms of it. One is focused attention, a sharp focus on a single task that can be sustained only for a few seconds. Another is sustained attention, which is directed at a single task for a longer period in order to learn and get things done. This is the type of attention that is most under threat today from distractions like social networks and the culture of so-called multitasking. If we train ourselves to stay focused on a single task for longer and consciously avoid multitasking, our efficiency will benefit significantly. The slip-box forces our attention onto a single task that should be completed before moving to the next, and therefore helps us to focus our attention for the required duration.
In writing, there are different roles to perform, each requiring a different type of attention. Writing a paragraph is fundamentally different from proofreading it. When proofreading, we need to take on the role of the critic, stepping back to review the structure and the flow of thoughts. It is difficult to express thoughts properly in the first draft, so it is easier to get the ideas onto the page first and improve them from there. It is easier to focus on finding the correct words first, without worrying about the structure, and to fix the structure later once the proper words have been found.
Outlining is yet another distinct task that requires a different type of focus, this time on whole arguments and the overall structure of a piece, rather than on individual sentences or word choices.
We should stop trying to be planners and instead become writing experts, relying on experience to master the process. An expert in writing understands the process and has developed an intuition for the order of tasks to perform in order to achieve their goals. To become an expert, we need to make our own decisions and the necessary mistakes that help us to learn and grow. There are several levels of experience, from competent performer to master, before someone is considered an expert. These people have internalized the necessary knowledge so that they do not have to actively remember the rules or think consciously about their choices; instead, they rely on intuition. This intuition can only be gained from systematic exposure to feedback loops and experiences. The slip-box provides a structure of clearly separable tasks that forces us to practice and gain the required experience.
Short-term memory is also a limited resource, and it is therefore necessary to have strategies to delegate information to an external system. Information cannot be saved in short-term memory like data on a memory stick; instead, it floats around in our heads, seeking our attention and occupying valuable mental resources until it is either forgotten or moved into long-term memory. There are techniques to increase the number of things we can remember, but these work by finding ways to bundle things together so they can be remembered as a single unit. It is easier to remember things we understand than things we do not.
Open tasks tend to occupy short-term memory until they are completed. That is why we get distracted by unfinished tasks, irrespective of their importance. However, taking a note and postponing a task for later is not distinguished by our brain from a task that has been completed. Writing down the task of writing into different, smaller tasks that can be completed gives the mind permission to think about specific ideas and allows us to pick up the work where we left off at any point in the future, without the need to keep everything in mind all the time. We can use this effect in the opposite way as well, by deliberately keeping unanswered questions in our mind so that we continue thinking about them and keep them in the central focus of our attention.
Another limited resource is motivation, which can deplete quickly and requires time to recover fully. There is some possibility of improvement through training, but it takes considerable time and effort. One way to deal with this limitation is to structure the work so that it can be done without the need to apply too much willpower. This means reducing the number of decisions that need to be taken, trimming decision-making to the minimum, for example by always using the same tools and following the same workflow, so that the bulk of our mental energy can be devoted to the actual intellectual tasks at hand.
Because the slip-box allows us to pick up the work at any point in time, it is possible to take breaks and resume the work from exactly the point where we left it, without loss of continuity or mental overhead.
Taking good notes while reading, notes that can later be inserted into the slip-box, accomplishes a substantial part of the work. What is really needed is simply to have a pen in hand while reading, so that the content can be translated into the different context of our own thinking and transformed later into our own ideas, ready to be inserted into the slip-box. The slip-box is an idea generator that develops alongside our knowledge, not just a storage system.
Once the ideas are in the slip-box, the final text becomes largely a matter of collecting the various notes and arranging them in linear order. The context is enriched, connections are made explicit, and from these notes the final result is created. When a note is written, it should never be just a copy of the text we have read. It must be a personal interpretation, because it will be used in a different context, our context. We need to express it in our own language so it can be reused within our own thinking.
Translating the idea into our own words requires understanding the deep meaning of the concept the author is trying to express. In any case, simply copying a quote verbatim already changes its meaning, because there is generally more context surrounding it that gets stripped away when the quote is isolated.
While reading, we should keep in mind what we already have in the slip-box, so that when taking a note, we might already have an idea of where it could fit within the existing structure. How extensive these notes should be depends on our ability to identify the core idea quickly and how fluent we are with the subject at hand. The main purpose of these reading notes is to support the next step, the writing of the actual slip-box notes.
Without a clear purpose for the notes, there is little incentive to take them, and to take them well. There is no particular fix style about how to take these notes, but it appears that taking handwritten notes results in a higher level of understanding of the subject compared to using a computer. The explanation could be quite straightforward: handwritten notes take longer, and this naturally facilitates the translation of what has been read into one’s own words.
Along with being selective, it is necessary to be selective in a smart way. The brain, by default, is not particularly smart in selecting information, because once a hypothesis is formulated, it scans the surroundings to find confirmation of it. Confirmation bias is something to always keep on the radar. Everyone is affected by it, and the best that can be done is to be aware of it and consciously try to do something about it. One good mental model is to deliberately try to find arguments against our ideas, ideally without too much mental effort and by embedding this practice into the standard workflow. The linear process of starting with a hypothesis about a topic to write about will almost certainly create confirmation bias. Conversely, developing arguments and ideas bottom-up helps us to look for insights, focusing on the most insightful ideas and bringing them forward in directions not preset in advance.
The important thing when using the slip-box is to make connections between the notes we put inside. Everything can contribute to the development of ideas within it, so we shift our attention from individual projects towards open connections within the slip-box. When looking inside, we can then be looking not only for confirming facts, but also for facts that give the opposite view. The slip-box does not have a particular bias built into the content we input; it is after the collection that we can draw our conclusions based on the data we have gathered.
The ability to select relevant information is another skill that requires learning and practice, and when taking notes, it is exercised many times each day. The more we practice it, the better we become at doing it. We are always looking for patterns in text, and as our skill improves, it becomes possible to read more quickly and with better comprehension. This needs to be a deliberate choice: we need to read selectively and be able to extract connections and references. Taking notes and rewriting what has already been written trains us to focus our attention on pattern recognition. The better we become at this, the more condensed and precise our notes will become.
Spotting patterns relates closely to critical thinking. Being able to rephrase questions and information allows us to understand more deeply the subjects we are investigating.
Taking notes is equivalent to giving a lecture to our future self, who, when reading the notes back, will likely have forgotten a large portion of the content. We should not underestimate the advantage of writing. When speaking, we can often get away with unfounded or unproven claims, but when concepts are put in writing, it is much more difficult to escape scrutiny. Reading can easily fool us into believing we understand the text and the context, but familiarity is not the same as understanding, and it is necessary to verify our understanding during our studies. Trying to explain a concept in our own words, in writing, shows immediately if there is any gap in understanding, and if there is, we must address it before moving forward.
Learning is a journey of understanding, and in order to demonstrate that we have understood, we need to test ourselves and retrieve the information from memory. Continuously rereading the same text is not the best way to learn. Choosing an external system that forces us to practice and exposes our lack of understanding as much as possible gives better learning results in the long run. Learning requires effort, and it is an individual task. It is impossible to have someone else learn on our behalf; we need to retrieve old knowledge and allow our brains to connect new ideas. Keeping a steady pace and a preset schedule, while at first glance appearing to help learning, can in the long run be an impairment. We need to put effort into retrieving information so that we can remember it in the long term.
Simply reviewing the same text is not a particularly effective tool for learning. The best method is elaboration, really thinking about the meaning of what we have read and how it can be combined with other knowledge. The slip-box ensures the storage of information and facilitates long-term learning. While it takes time to take notes and sort them into the slip-box, this is a necessary elaboration that ultimately makes us learn. The slip-box contains the information as a form of long-term memory, and the brain can focus on the ideas, the deeper understanding, and the connections.
Experienced readers usually read a text with questions or topics in mind, trying to relate it to other ideas or approaches. Good readers can identify the limitations of a particular approach or notice what is not written in the text, the gaps and assumptions left unspoken.
Therefore, writing notes instead of simply copying quotes is beneficial, especially when the goal is to connect these notes with other ideas. This is precisely what the slip-box is all about: when we write and add permanent notes to the slip-box, we are linking them with other notes in a chain of thought.
While writing a long text at once might be intimidating, writing a shorter one is generally perceived as manageable. There is no fixed quota to be produced, but in general people underestimate the time that writing a specific text will take. This happens constantly, whether writing content for a website, composing emails, or drafting notes.
The slip-box operates as a compounding machine, because the value of the slip-box content is worth more than the sum of the notes contained within it. The connections between notes create emergent value. All of this can start from just a few notes each day, which is surely a manageable task.
Taking notes gives us immediate feedback about whether we have understood the subject or not, and moving to permanent notes tests our understanding even more, as it requires thinking more deeply and creating connections with already existing notes. Writing with existing notes in mind requires taking into account information that is already available in our memory, so these memories are retrieved, expanded, and rewritten. Because the brain tends to jump to conclusions, writing things down ensures that the thinking process is completed. We could even put in the slip-box the precise reason why we are reading a book in the first place and what we are expecting to gain from it.
Taking smart notes is the first step to increase the chance that we will remember what we read in the long term. A further step is to transfer those ideas into our network of thoughts, so we can elaborate on them within different contexts and connect them to other ideas. Transferring ideas into external memory allows us not to forget them, or more precisely, it allows us to forget them temporarily but to pick them up again when needed, so that they can move into long-term memory. Forgetting might not be the loss of a memory, but rather a mechanism that evolution created to separate the conscious mind from our long-term memory, to prevent our brain from being constantly flooded with irrelevant memories. Subconsciously, there is a mechanism in place that inhibits the storage of every memory except a limited number that are helpful in a given situation. Unlike a computer hard disk, we cannot simply choose what to store. Learning appears to be more about building connections between different pieces of information, so that they can be retrieved when they are needed.
The way we can grow this retrieval strength is by using the slip-box, because we can connect a single piece of information with many contexts, and these interconnected ideas work as cues for each other. From an evolutionary perspective, focusing on meaningful connections makes sense. People who can remember a huge number of details, such as the names of all people attending a dinner, attach meaning to information they already know, creating cues for new information, for example using techniques like the memory palace.
As mentioned before, learning is understanding, so the main objective is to understand, to store meaningful information. Once learned in this way, it is almost impossible to forget, and the information can be retrieved on demand if the relevant cue is triggered.
Writing notes for the slip-box forces us to ask questions and find hidden meanings and connections. Since the slip-box is not sorted into rigid categories, there are no preconditions for building connections, giving us freedom and space for exploration.
After the permanent notes are written, they can be added to the slip-box. They are then numbered and inserted in the position that feels most appropriate, links are added to other notes, and finally we ensure that they can be reached from the index, either directly or through a chain of notes connected to the index.
AHRENS, Sönke, 2017. How to Take Smart Notes: One Simple Technique to Boost Writing, Learning and Thinking – for Students, Academics and Nonfiction Book Writers. North Charleston, SC: CreateSpace Independent Publishing Platform. ISBN 978-1-5428-6650-7.