Luhmann’s Zettelkasten — A Productivity Tool That Works Like Your Brain

  1. November 2019

Niklas Luhmann was a german sociologist and system theorist. Born in Lüneburg, Germany in 1927, he spent most of his life studying the socio-ecological structure of societies, being one of the most important scientists of the 20th century in this field. Furthermore, he is considered to be one of the most productive scientists yet. In his career, he wrote about 60 books and other documents without the help of assistants. An impressive amount of publications.

Niklas Luhmann

Niklas Luhmann (born on December, 8th 1927, died on November, 6th 1998)

How could he be so productive and how did he manage to keep track of his knowledge? After reading this article you will know how he did it and how you can implement his method for yourself.

The Zettelkasten

Luhmann used the Zettelkasten (“slip-box”) to sort his mind. A simple but powerful tool for organizing information and thinking. Luhmann claimed that the Zettelkasten is responsible for his productivity. His Zettelkasten contains about 90.000 cards and now belongs to the University of Bielefeld after they bought it from Luhmann’s children. You can take a look at it by visiting the university website. They have digitized the whole Zettelkasten.

A Zettelkasten (die Zettelkästen in plural) is a methodology for thinking in writing. It combines note-taking while reading, personal thoughts and a bibliographic system.

As a tool, the Zettelkasten is a box (or a box of boxes) to hold index cards or slips of paper (“Zettel”). Each card holds a piece of information, an index and the source of the information. The index can be an ongoing number, the date and time or anything else you can use as a unique identifier. The information is a short note in most cases and should be limited to a few words or sentences. The size of the card helps to keep it brief. Drawings and other forms of information can be used too.


An example of a Zettel about Gleichheit (“equality”) taken from Luhmann’s Zettelkasten.

The cards are then arranged inboxes. Each box contains a set of cards that are related to each other. The boxes are labeled by a broader topic or a time period, depending on what you’re writing, like a history book for example.

Inside a box, cards can be organized further by placing tabs with keywords in between, so that you can look up cards more easily inside large boxes. Luhmann did not use tabs.


Luhmann’s Zettelkasten at the University of Bielefeld.

As you fill your Zettelkasten, you will add more and more cards. To unleash its full potential, cards must be linked manually by using the box label, keywords and the card index you’re referring to. Cards can be linked with none, one or multiple other cards. To connect them you will have to search and traverse the Zettelkasten’s structure a lot, which is part of its design and brings some of the key benefits.

The process of linking cards is intended to work similarly to your brain. By connecting lose dots of information you create interconnected clusters of knowledge that emphasize the importance of information based on the number of connections. It also helps you to remember where you can find a piece of information. Interlinking information accelerates lateral thinking and the overall value of your Zettelkasten. The limited size of a card encourages knowledge to be developed by its connections rather than its content. If it’s not linked strong enough, it might get lost, which means it was probably not that important. Once you’ve written down information or thought and linked it to relevant cards, you can drop it from your mind and come back to it later. The thinking in writing allows you to resume and pick it up again where you have left it.

Here is a quick summary of the parts:

  • cards are used to store a piece of information
  • the card index is used to identify a card
  • cards are linked by using their card indexes as references
  • cards are grouped into broader topics by sorting them into boxes
  • boxes can optionally be split by tabs with keywords on them, to improve scanability

Working with your Zettelkasten

Luhmann once said that if you would use some sort of structure (like the table of contents in a book for example), you commit to a fixed sequence that affects your thinking and limits the possible paths your knowledge base might take. This is why the indexing system you chose is important for the expandability of your Zettelkasten. It is crucial to be flexible when assigning new indexes, to insert a new card between two existing cards for example, while retaining meaningful indexes. The index system is the backbone of your Zettelkasten.

So, what is a good indexing system? Luhmann used hierarchical indices, which allowed him to add new cards everywhere in his structure and keep them in order at the same time. We start with a very basic Zettel structure, containing just three cards.

Step 1

A simple Zettelkasten structure.

As you can see, the cards are provided with a consecutive number. If we would like to go into more detail on card number 2. We could do that by adding card number 2a and continue the row with card numbers 2b, 2c and so on.

Step 2

Adding more detail to the Zettelkasten.

In case we now would like to go into more detail on one of the deeper cards, we just start over with a new sequence beginning at 1. This could go on forever if you so desire. In the end, we have a structure that provides a quick and relatively small overview of our knowledge base but goes into detail if you follow a path. The structure can also be flattened to create a flow of information that can be written down in a book, for example.

Step 3

Flattening the Zettelkasten structure.

Note that the cards of your structure might be spread across multiple boxes. The cards that are part of a box and don’t have a parent card are good starting points of your investigation. A Zettelkasten can also surprise the creator himself and perhaps bring to light links that he would never have thought of.