- Fleeting notes, captured while reading or consuming a source, and which serve as reminders of information. These can usually be trashed before too long.
- Permanent notes, written such that they will be perfectly legible apart from their original context and as if they are ready for print
- Project notes, which pertain to a specific project and are disposable once the project is complete
Some approaches to zettelkasten include "literature notes," a phase between fleeting and permanent notes. But, it's not clear if Ahrens sees these as distinct from permanent notes as he describes them in this taxonomy. On the Zettelkasten.de form, user @Will offers his take, which is that permanent notes are permanently useful and not conditional on source or originality.
Notes should never be copied verbatim. Rephrasing ideas creates an immediate feedback loop: it requires one to wrestle with the idea and ensure that they understand it enough to articulate it in a new way. This requires understanding. (See Writing is thinking.)
Luhmann, Niklas. “Communicating with Slip Boxes.” Translated by Manfred Kuehn. Two Essays by Niklas Luhmann. Accessed October 19, 2020. https://luhmann.surge.sh/communicating-with-slip-boxes.