Zettelkasten: A Thinking Tool

Niklas Luhmann (1927–1998) was a sociologists. All in all, he wrote 50 books and 550 articles. The number of publications is unprecedented in contemporary sociology.¹ The large number of publications would have been impossible without his filing system (Zettelkasten, or anteckningslåda in Swedish).²

Of course, I do not think of all this on my own; it mostly happens in my file. … In essence, the filing system explains my productivity. … Filing takes more of my time than writing the book.

Niklas Luhmann ³

Luhmann made notes on what came to his mind in the process of reading. He always asked himself how what he read could be integrated into the Zettelkasten. After he had completed his reading, he prepared the notes and decided where to insert them into the Zettelkasten. The position of a note was decided in relation to the other notes.⁴

Luhmann called the Zettelkasten his ‘secondary memory’? He perceived it as a thinking tool that could give surprising answers, even if person who asked was the author of the note. This was accomplished by the positioning of each note in combination with an internal system of references, and a comprehensive keyword index (see below).⁵

The Zettelkasten is an aggregation of a vast number of notes on specific concepts and topics.⁶ When Luhmann came across an idea about one of his notes, he inserted an additional note in the sequence of notes. This could be done again and again, which enabled the collection to grow.⁷

Luhmann organized the notes based on the principle that they must have some relation to another note. There is no privileged position in the web of notes.⁸ The notes may be inserted in different places and different contexts.⁹ Luhmann deliberately avoided a fixed system of order. His approach allowed the collection of notes adapt to his thinking.¹⁰

Luhmann’s Zettelkasten is not built on content, but on positioning.¹¹ Each note is given a position in relation to other notes.¹² There are three different types of references to other notes:¹³

1. References in an outline form. This resembles a table of contents.
2. Collective references to a subject matter.
3. Single references to another aspect or idea.

Each note…derives its quality from the web of references and cross references within the system.

Niklas Luhmann ¹⁵

Accessing the Zettelkasten via the keyword index does not limit the search to the exact word. The references open up a web of notes.¹⁶ Referencing leads to other subjects and creates connections to other aspects or ideas.¹⁷

Writing things down enables disciplined thinking. The evolution of the Zettelkasten reflects the thought process. Original ideas were never removed, and new or revised ideas were added as needed.¹⁸

The Zettelkasten was not only a thinking tool but also a publication machine. The book format makes the great depth of the Zettelkasten accessible. A book or an article inevitably reduces the number of references that can be traced due to limited space and the linear mode of presentation.¹⁹

Notes:
1. Johannes Schmidt, Niklas Luhmann’s Card Index: Thinking Tool, Communication Partner, Publication Machine, in Cevolini, Alberto (ed.). Forgetting Machines: Knowledge Management Evolution in Early Modern Europe, p. 289. Archived (PDF) from the original on 2020-11-27. Accessed 2022-10-20.
2. Ibid., pp. 290–291.
3. Niklas Luhmann, Biographie, Attitüden, Zettelkasten, p. 142f
4. Johannes Schmidt, Niklas Luhmann’s Card Index, p. 293.
5. Ibid., p. 295.
6. Ibid..
7. Ibid., p. 298.
8. Ibid..
9. Ibid., p. 299.
10. Ibid., p. 300.
11. Ibid..
12. Ibid., p. 301.
12. Ibid., p. 302.
13. Ibid., pp. 302–303.
14. Ibid., p. 305.
15. Niklas Luhmann, Kommunikation mit Zettelkästen, p. 225.
16. Johannes Schmidt, Niklas Luhmann’s Card Index, p. 307.
17. Ibid., p. 309.
18. Ibid..
19. Ibid., p. 311.