Niklas Luhmann didn’t invent the zettelkasten, Rather, he developed a unique way to use it the structure of Luhmann’s style zettelkasten is not predetermined. it merges out of the relationships the note maker establishes between ideas recorded in the notes.
As relationships develop, areas of the zettelkasten swell, common topics and themes emerge and are recorded in additional notes or otherwise indicated in the system, with Luhmann’s style zettelkasten we begin with neither a predefined set of categories to which notes should be assigned nor do we store our notes in the topical folders.