Method
Zettelkasten, without the mystique
A Zettelkasten is a note system with three rules: one idea per note, written in your own words, and linked to the notes it relates to rather than filed under a topic. Niklas Luhmann kept his on paper index cards. Digitally, the method needs cheap linking, stable note identity and a way back in — which is what wikilinks, backlinks and index notes provide.
The three rules, and why each one is there
- One idea per note. Atomic notes can be linked precisely and reused in contexts you did not anticipate. A note containing six ideas can only ever be linked as a lump.
- In your own words. Rewriting forces comprehension. A note that is a quotation is a bookmark; a note that is your restatement is a thought you have actually had. This is the rule people skip and the reason their system feels inert.
- Linked, not filed. Rather than assigning a category, you connect the note to the existing notes it argues with, extends or contradicts. The structure is emergent — it is the record of what you noticed, not a taxonomy you invented in advance.
What Luhmann's numbering was actually for
Luhmann's famous alphanumeric ids — 21/3d7a6 — get treated as the heart of the method. They were a workaround. On paper, a new card had to be physically placed somewhere, and the numbering let him insert a card next to the one it responded to without renumbering the box.
Software removes the constraint entirely: a link is a link regardless of where a note sits. Reproducing Luhmann's ids in a digital system is cargo cult. Keep the atomicity, the rewriting and the linking; drop the numbering.
Fleeting, literature, permanent
The three-tier distinction is worth keeping because it prevents the most common failure: a slip-box full of quotations nobody will ever reread.
Fleeting notes are captures — a thought on a walk, a line from a conversation. They are disposable and should be processed within days. Literature notes record what a source said, in your words, with the citation. Permanent notes are the actual Zettelkasten: one idea, your own claim, linked into the network. The work is the promotion from one tier to the next, and skipping it produces a very tidy archive of things you have not thought about.
Index notes and the way back in
A network with no entry points is unusable. Luhmann kept hub cards pointing into each line of thought; the digital equivalent is variously called an index note, a structure note or a map of content. It is a note whose body is mostly links, curated by hand, describing a region of the vault.
Build them when a cluster gets big enough to be hard to hold in your head — not before. A map of content written on day one is a folder hierarchy wearing a different hat.
Running one in Nodum
Practically: one note per idea, titled as the claim it makes rather than the topic it covers ('Compound interest rewards patience more than accuracy' beats 'Compound interest'). Link with [[ as you write. Let the backlinks pane show you what already argues with the note you are on. Use tags for state — #fleeting, #literature, #permanent — rather than for topics, since topics are what links are for.
The graph earns its place here specifically: orphans are notes you captured and never thought about again, and dense clusters with no edge between them are two lines of thought that have never met.
Questions people ask
What is a Zettelkasten?
A Zettelkasten — German for 'slip box' — is a note-taking method built on atomic notes: one idea per note, written in your own words, and linked to related notes rather than filed by topic. It was made famous by the sociologist Niklas Luhmann, who used it to write a very large body of work from a box of index cards.
What is the best app for a digital Zettelkasten?
Any app with cheap wikilinks and automatic backlinks will do: Obsidian, Logseq, Roam and Nodum all qualify. Nodum is the open-source, browser-based option — MIT licensed, plain markdown, wikilinks with autocomplete, automatic backlinks with context, and a knowledge graph for spotting orphans and clusters.
Do I need Luhmann's numbering system?
No. The alphanumeric ids solved a physical problem — inserting a card next to a related one without renumbering the box. In software, links do that directly. Keep the atomic notes, the rewriting in your own words, and the linking; the numbering adds nothing.
Related reading
Comparing specific tools
- Nodum vs ObsidianNodum is a free, MIT-licensed Obsidian alternative for the web: same [[wikilinks]], same backlinks, same graph — no install, and you can read the source.
- Nodum vs NotionNodum is a free, open-source Notion alternative built on plain markdown, [[wikilinks]] and a knowledge graph — self-hostable, exportable, no per-seat pricing.
- Nodum vs LogseqNodum and Logseq are both open source and both link notes. Nodum is a document editor in the browser; Logseq is a local-first outliner. Here is the honest split.
All 18 are on the alternatives index. Terms used on this page are defined in the glossary.
Start tying things together.
A vault takes about ten seconds to make. Bring notes with you, or start with one.