Slip-box
The Zettelkasten method of note-taking is designed to increase research productivity: in particular, it acts as a research partner, where conversations with it may produce new and surprising lines of thought. This method is attributed to German sociologist Niklas Luhmann, who using the method had produced volumes of written works.
In its paper form, the slip-box is simply a box of cards. These cards are small – often only large enough to fit a single concept. The size limitation encourages ideas to be broken down into individual concepts. These ideas are explicitly linked together. The breakdown of ideas encourages tangential exploration of ideas, increasing the surface for thought. Making linking explicit between notes also encourages one to think about the connections between concepts.
There are two kind of notes: fleeting notes and permanent notes.