A Zettelkasten-style note method: fixed numbers, branching and a keyword register

What it is

In "Communicating with Slip Boxes" the sociologist Niklas Luhmann describes the card file he wrote for decades. Its central decision is to reject ordering by topic and instead give every slip a fixed number that never changes. From that decision he derives three properties: arbitrary internal branching (a slip 57/12 is continued by 57/13 but can be supplemented at any word by 57/12a, 57/12b, and those again by 57/12a1); cheap linking, since a reference to a fixed number stays valid and back links can be recorded on the target; and a keyword register, because without a topical order the notes must be rediscovered through an index that is constantly updated. Bibliographical slips live in a separate box, one per work actually read, with numbered links to the notes that came out of it.

Why it matters

A topic hierarchy forces a decision about where a note belongs before its use is known, and every reorganisation breaks the links into it. Fixed identifiers separate the address of a note from its meaning, so the collection can grow in directions the author did not foresee. Luhmann calls the result a "secondary memory" with no hierarchy and no linear structure, which, in his words, gets a life of its own independent of its author.

How to apply

• Give each note one identifier that is never reused or renamed: a timestamp (20260916T0914), a sequence number, or Luhmann's branching numbers. The file name carries the identifier; the title may change.
• Write one idea per note in your own words, with the source reference on the note. Copied passages are marked as quotations.
• When filing a new note, place it next to the note it continues and write the link in both directions; do not look for the "right" folder.
• Keep a register: a single index file mapping keywords to identifiers, extended whenever a note is written. In a plain-text collection a full-text search complements the register but does not replace it, since the register records which notes the author considered entry points.
• Keep one literature note per source, listing which notes it generated.

Pitfalls

Collecting instead of thinking: a note that merely files a fact without a connection to an existing note adds nothing the search engine could not. Links without a sentence saying why they exist. Renaming identifiers "to tidy up", which breaks every reference. Tool features (backlink panels, graphs) tempt one to skip the register and the written connections, which are the part that carries the method.