I believe the most central aspect of Luhmann's Zettelkasten was the radical rejection of hierarchical organization as you might find it today in outliners, for instance where the information is arranged under headings, like so:
Philosophy Epistemology Realism Metaphysics Materialism Idealism objective idealism Plato Kant Hegel subjective idealism Berkeley etc., etc.
Instead, Luhmann opted for a non-hierarchical organization by giving every note (Zettel) a unique number that corresponded and indicated the physical place of the note (Zettel) in the boxes in which they were stored. This is in some ways like the call numbers according to which libraries organize their book collections, like the Dewey decimal system or, better, that of faceted classification by Ranganathan.
This approach allowed him both to refer to each of the notes by a fixed number and to find the physical piece of paper by its location in the Zettelkasten. So 1 was followed by 2, 3, 4, etc. His convention allowed him to have have several notes that continue any note. So 1/1 and 1/2 continue 1. Obviously, an electronic version of the Zettelkasten that has no built-in limitation on the length of notes can do without such continuations (but it does not have to do without continuations either). Daniel Luedecke's Zettelkasten sports "Folgezettel" or "continuations." They seem to implement that feature.
Secondly, Luhmann's approach allowed him to branch off any topic that seemed necessary to him. So, a note on "objective idealism" could branch to both "idealism" or "transcendental idealism" or "subjective idealism." Luhmann indicated branches by letters (a, b, c etc.). Combinations of continuations, branches, and continuations of branches could lead to expressions that are just as forbidding as the call numbers of library books. There are no limits to the number of physical objects you can refer to by these scheme. Luhmann's system is a freely expandable collection of interlinked notes. It resembles a hypertext system for storing and modifying information where each page is easily reachable from any notes. It is as well as you could do in a paper-based system, I would say.
How Luhmann actually assigned numbers is not important, as far as I am concerned. It was important for his physical implementation of the Zettelkasten. It is far less important for an electronic version as a database in which every record automatically gets assigned a number already. If you decide to use a non-database version by implementing it in plain text, for instance, you need fixed numbers again. But the exact time and date of when the note was taken might be sufficient (see Christian Tietze's approach for this, i.e. search for him in this blog and follow the links).
I have decided for a database or a personal wiki which is "a freely expandable collection of interlinked ... 'pages,' a hypertext system for storing and modifying information — a database, where each page is easily" reachable from any other page.Furthermore, the notes which are static in a paper system are freely editable.
You reach any note simply by enclosing the name of the note by double brackets, like so "[[objective idealism]]". In other words, you can directly link to any other page directly. And without the interference of numbers, as Tietze's system still seems to oblige you to do, or the interference of keywords or tags, as Luedecke's Zettelkasten and many other note-taking applications require you to do. Let my quote Caulfield again:
At the heart of wiki is a simple idea that names matter. Page names in wiki are not locations. They aren’t a place where a document lives. Names identify ideas, patterns, theories, and data in wiki that can be recombined with other ideas, patterns, theories, and data to make complex meaning not expressible in a normal text.The same holds for having to add reference numbers or key words. They break the flow, slow you down and get between you and the ideas, patterns and theories--or so I would hold.
If you’ve ever had a good wiki experience, you know what this feels like in practice. Groping towards an idea on one page you realize its relation to another page and quickly make a [[Bracketed Link]] or CamelCaseAssociation to pull that idea into your web. But most non-wiki environments frustrate this fluidity. They don’t want to know the name of the page — they want to know its location, which is like asking someone to give up using variables in their code and start addressing memory directly. It can be done, but it is going to kill your flow.
I have nothing against tags or categories per se. ConnectedText, the personal wiki software I use, allows you to freely assign as many as you want. But they are not the primary way of organizing your stuff. The same could be said of numbering schemes. Nor do I have anything against search. ConnectedText has a very capable search engine. But, again, I would not want to have to have to rely on search alone to navigate a system of 10,000 notes, or more.
In any case, as I have said many times before, I believe a personal wiki, or, more generally, a personal hypertext system best captures the spirit of Luhmann's system because it allows names to "identify ideas, patterns, theories, and data in wiki that can be recombined with other ideas, patterns, theories, and data to make complex meaning not expressible in ... normal text." It is no accident that many people discussing Luhmann's Zettelkasten have characterized it as a precursor to hypertext.
I should perhaps add that I consider my approach in no way as the alleinseligmachende (or exclusively salvatory) approach to note-taking. It may, indeed, be just my highly idiosyncratic way of doing things. So, take my advice (just as the advice of anyone else) cum grano salis.
1. I do believe that if you write more than 500 words, you are usually not going on in the same way on the same subject, but are making different points that deserves a new note.
2. The quote is from Bo Leuf and Ward Cunningham.