stop thinking so hard about zettelkasten numbering

MAY 16, 2026

note-taking

Anyone sufficiently interested in note-taking will eventually stumble upon Niklas Luhmann's Zettelkasten, purportedly responsible for Luhmann's prolific output (the man wrote something like 70 books and 400 articles). The Zettelkasten system is a favorite of the note-taking community, with dedicated users (including myself!) implementing Luhmann's system in programs like Obsidian.

In the Zettelkasten system,1 the unit of note-taking is the Zettel — a note that houses exactly one idea. Once you have your Zettels, you hyperlink them together, emphasizing how they are connected to each other. The emphasis on connections encourages you to spot parallels between seemingly unrelated ideas, which in turn helps you generate novel insights.

But the most distinctive feature of the Zettelkasten system is that each Zettel gets a unique alphanumeric identifier. Initially, you just count up: the first note gets a 1, the second note gets a 2, etc. These notes live in order like this:

[1]

[2]

But once you want a note to be between notes 1 and 2, you add a second position to the address to get 1a. Then sorting alphabetically gives this:

[1]

[1a]

[2]

You can then continue from 1a by incrementing the last position to get 1b, 1c, and so on. Then if you want a note to live between 1a and 1b, you can add another position, a number this time, to get 1a1. You can continue to put any note between any two other notes by adding more positions, alternating between numbers and letters. (fun fact—this means that the Zettelkasten numbering system is dense!)

But there's a bit of ambiguity here. Once you have 1, 1a, and 2, you could put a note between 1a and 2 in two ways: by using 1b or 1a1.

[1]

[1a]

[1b]/[1a1]

[2]

So when should you increment the address, and when should you append a new character?

The classical answer is something like this (from zettelkasten.de):

So, in short, whenever you continue a train of thought, you increment the last position in the address, be it number or a character from the alphabet. And when you want to expand, intersperse, or comment on a note, you take its address and append a new character. For this to work, you alternate numbers and characters.

The idea is that you should distinguish between "continuing a train of thought" and "expanding, interspersing, or commenting on a note" and use that to determine a Zettel's number.

Hot take: this distinction is irrelevant. You should not think about it.

First of all, you can't know a priori whether you're going to be doing one or the other. Sometimes I start a note that continues a train of thought I was having, but then further research reveals that my original premise was totally wrong. My note then turns into an "oh man the last note was totally wrong about all things" note — a comment on the previous note. I don't necessarily know which one I'm doing midway through the note, either; in the process of creating one note, it's not uncommon for me to flip back and forth between the "continuing a train of thought" and "expanding, interspersing, or commenting on a note" multiple times.

Sometimes, you can't know even when you're done with the note. One of the notes in my Zettelkasten is about Tummo breathing. Learning about Tummo breathing made me think about how bodily functions might be under more conscious control we think, so I have a note for that, too. Is this second note continuing a train of thought? For sure. But it is also commenting on the broader implications of the content in the first note. When you come across such obvious ambiguity in a pattern as common as "I came across a fact and then I thought something about it", it's clear that the "continuing a train of thought"/"expanding, interspersing, or commenting on a note" distinction is a false dichotomy.

Besides, trying to determine whether a note is one or the other on some Platonic ideal level is a fool's errand. You want to be taking notes, not thinking about taking notes. The strength of the Zettelkasten numbering system is that it adds physicality to your notes without the friction of explicit categorization — don't reintroduce friction at creation time.

why even bother with the numbers?

Let's back up for a second. What's the point of using the Zettelkasten numbering at all? Luhmann's original Zettelkasten was a physical box of index cards, so he needed numbers to catalogue his Zettels. Some people still use phyical slip-boxes — there's a whole subreddit full of them — but if you're a Modern Human Being like me, you make and store your notes on a computer. Why use catalogue numbers when you can search your entire corpus of notes at will? These days, you could even leverage LLMs to pull a "JARVIS, find me all my notes on that one TikTok sea shanty craze" if you wanted. On top of that, you have infinite freedom in Abstract Computer Land to arrange your notes in any way you see fit.

But infinite freedom is itself the problem. The brain was not meant to interface with Abstract Computer Land — it likes things it can touch and see and make sense of in physical space. That's why the flat, tag-and-link style of "second brain"- or PKM-type systems feels so ephemeral. My own experience with these systems went something like this:

  1. Write a note and make some links. (great!)
  2. The note disappears into the ether, unmoored to reality.

Because there was no physical structure around the notes, I had difficulty locating things that I had written. My own notes ceased to exist to me, and herein lies the problem: you can't search if you don't know what there is to search.

The benefit of Zettelkasten numbering is that it's loose enough to retain the freedom of tag-and-link systems, while still allowing you to locate specific "blobs" of concepts in physical space. As in a tag-and-link system, you don't have to figure out how to categorize your note. You simply give it a number and write. Despite this, the notes live in a canonical order, giving you an anchoring physical metaphor. You can remember the general location of a note, in the same way you remember the general location of π\pi on a number line. As a plus, you get natural groupings of related ideas, which allows you to "browse" your notes like books on a library shelf.

Thinking very hard about how you should number a note doesn't give you any benefit in physicality. It's like this: when you mark π\pi on a number line, you don't meticulously measure to put it at exactly 3.14159…3.14159\dots. You just put a mark "somewhere between 33 and 44, closer to 33". Similarly, there's no point in fussing over the exact order of your Zettels. It's enough to know that your new note will stay somewhat near the original note, which will be the case whether you choose to increment the address or append a new position.

wait but what about folders

If you're looking to add physicality to a digital system, though, your first thought wouldn't be Zettelkasten numbering. It would be files and folders, which is the dominant physical metaphor in every operating system.

The problem with the file-and-folder paradigm is that it introduces far too much friction when all you want to do is just make notes. You have to make all these decisions that are unrelated to the ideas you actually want to think about.

For example, when does a concept deserve a new folder? There is certainly a point where a folder is too big to be useful; the strawman here is a "notes" folder where you can't find anything, but it can obviously happen with any folder once you make enough notes. Similarly, it is absolutely useless to have a million folders, each containing exactly one note. But in real life, you don't collect knowledge in clearly-demarcated semester-long classes. You don't know you don't know what knowledge you will come across when and you don't know what notes you'll make in the future, so there's no way to tell what folders will be useful to you later. You just have to commit to reorganizing your notes every so often, which gets harder and harder the more notes you make.

There's more. What happens when you have ambiguity about where a note should go? A note about whether humans are eusocial or not, for example, would be somewhere in the intersection of evolutionary biology, anthropology, and cultural studies. Choosing one is committing to viewing that note through a specific lens. Except, like we said, you don't know what you're going to be thinking about in the future. If you ever decide to take your notes in a different direction, you'll either have to live with them living in the wrong folder, or have to do a bunch of reorganizing. This sucks. You want to be making notes at the intersection of different fields — these are the notes that represent novel ideas and connections! — but you're actively adding friction to the process.

The rigidity of the folder system pre-constrains your thinking, making it easier to makes notes that fall into someone else's pre-defined categories, and harder to make notes that don't. Trying to decide how to number a Zettel based on the "continuing a train of thought"/"expanding, interspersing, or commenting on a note" distinction has the same problem. You're making it harder to see the thoughts that aren't cleanly one or the other, and for what? To be able to track whether a note is one or the other, when this isn't a useful distinction anyway?

just take the easy way out

The key benefit of Zettelkasten numbering is that it adds physicality without the friction of folder-based organization. Don't add the friction back in by attempting to taxonomize notes when you don't have to; choose whatever system that will make it easiest to slap a number on a Zettel.

Here's the little algorithm that works for me:

  1. if you were working off of a related note2, increment the last position of that note's address
    1. if a note with this address doesn't exist, done! use this address
    2. otherwise, append a new position to the previous note's address
  2. if you weren't working off of a related note, skim/think for ~10 seconds to see if you can come up with one
    1. if you can, go back to step 1
    2. if you can't, give the new note the next available top-level address (i.e., single-number address)

Basically, it's "exact position is irrelevant" and "prefer incrementing last position, adding new position only if necessary".

This is all you need. Stop thinking so hard about the numbering, and think harder about what you actually wanted to think about.

footnotes

  1. Technically, the term "Zettelkasten" refers to two things: Luhmann's particular system and a broader system for collecting quotes and notes through index cards. Since online discourse centers on Luhmann's system, that will be the focus of this post. ↩

  2. If you were thinking about multiple notes, pick the one that's nearest to the top. Or pick one at random. It doesn't matter. ↩

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