The Luhmann Method
Although people call it the Zettelkasten method , I think it is way more appropriate to acknowledge its creator, Niklas Luhmann. The method is relatively simple, write down notes on pieces of paper (short notes), number them, and place them in boxes 1 . Next time you put a note, decide after (or before) which other note you want to place it.
If you have a note numbered 22, and one numbered 23, you could slip a note between them with the number 22/a, for example. This can grow in complexity and branches, such as 22/a1, 22/a2 could admit a note in between them, for example 22/a11. Complexity emerges from a mindful organization of notes and not from a top-down imposition.
In this system, the placement of the notes is crucial to build knowledge. An index could point to the starting point, to make it easier finding where to place a note.
These are the other notes that link to this one.