Zettelkasten

Zettelkasten ("slip-box" in German) is a note-taking method popularized by sociologist Niklas Luhmann. Each idea gets its own atomic note with a unique ID; notes are linked to each other, building an interconnected web of thinking rather than a tree of folders. Luhmann credited his prolific output — 70+ books, hundreds of papers — to the slip-box, which he described as a thinking partner rather than a filing system.

The method's core principles: one idea per note, link aggressively, never throw anything out, but never keep everything verbatim — rewrite incoming material in your own words. Modern PKM tools like Obsidian, Logseq, and Roam Research are essentially digital Zettelkastens. The approach directly inspired evergreen notes and digital gardens, and is one of the intellectual roots of MOC-based navigation.