A [Zettelkasten](https://en.wikipedia.org/wiki/Zettelkasten) is a system for note taking that was invented by [[Conrad Gessner]] in the XVI century, and consists on using small [[atomic notes]] that are heavily interlinked. The connections in a Zettelkasten are its differencing factor: these connections are in charge of organizing the content, since (in its most orthodox understanding) **a Zettelkasten should not have any kind of hierarchy - just links**. As John Locke writes in his *Essay of Concerning Human Understanding*, > The acts of the mind, wherein it exerts its power over simple ideas, are chiefly these three: > 1. Combining several simple ideas into one compound one, and thus all *complex ideas* are made. > 2. The second is bringing two ideas, whether simple or complex, together, and setting them by one another so as to take a view of them at once, without uniting them into one, by which it gets all its ideas of *relations*. > 3. The third is separating them from all other ideas that accompany them in their real existence: this is called abstraction, and thus all its *general ideas* are made.