[the notes from the book were retrieved with kobogarden, with the purpose of aiding to create a map of the ideas the book left me. The full list of book highlights can be found here.]

This is the book that brought the notion of second-brain to my understanding; Ahrens is motivated by letting us know how to manage, and thrive in, the enormous amounts of information and knowledge stimuli, with an approach that is directly influenced by Zettelkasten, of which Luhmann's example is explored with more detail. I kept the book at bay for years, and finally caved in — my notes on it are, unfortunately, assembled appalingly late.

(of course, I now tried to organise the notes and ideas in the best possible way while reading the book — so, well, it's an amusing (meta-?)exercise on learning about and improving my writing — Søren even frequently tiptoes on material that one would easily associate with Douglas Hofstaeder's musings on consciousness — but I digress).

The book (henceforth referred to as HTSM) is not just a set of instructions on how to do Zettelkasten; it also touches on adjacent theories of psychology, productivity, and cognition, and does so with extensive mentions of relevant academic studies that support his theories (it is also clear that the book is, itself, a product of the method).

reading as an active act of discovery and inquiry

Being a good, curious reader does not guarantee being capable of following up on ideas. Whenever we read (especially in the context of non-fiction, and likely, but not necessarily, academic work), it should be an active task of engaging the text, integrating it with our own ideas. Notes should be taken so as to later contribute to the critical mass arising from the slip-box. More on that in a few moments: first, Ahrens argues very early in the book that reading is an exercise with pen in hand, and recalls one example from Luhmann himself:

Luhmann describes this step as follows: “I always have a slip of paper at hand, on which I note down the ideas of certain pages. On the back, I write down the bibliographic details. After finishing the book, I go through my notes and think how these notes might be relevant for already written notes in the slip-box. It means that I always read with an eye towards possible connections in the slip-box.” (Luhmann et al., 1987, 150) How extensive the literature notes should be really depends on the text and what we need it for.

Luhmann's direct citations are spread throughout the whole work. As Ahrens conveys the slip-box system, we get further insights into why it works and how it can help produce novel, robust ideas based on other writings and research. It is fundamentally tied to acts of learning and cognition. Another Luhmann quote sheds light on the need for such a system: one that puts rewriting and active dialogue with other ideas at the forefront.

(a tangential anecdote via Feynman, and I think it is the third time I see it in writing:)

Richard Feynman once had a visitor in his office, a historian who wanted to interview him. When he spotted Feynman’s notebooks, he said how delighted he was to see such “wonderful records of Feynman’s thinking.” “No, no!” Feynman protested. “They aren’t a record of my thinking process. They are my thinking process. I actually did the work on the paper.” “Well,” the historian said, “the work was done in your head, but the record of it is still here.” “No, it’s not a record, not really. It’s working. You have to work on paper, and this is the paper.” This, obviously, was a very important distinction to Feynman, much more than just a linguistic difference – and for a good reason: It is the distinction that makes all the difference when it comes to thinking.

the possible kinds of notes

Let's establish the only three kinds of notes to be considered:

To achieve a critical mass, it is crucial to distinguish clearly between three types of notes:

1. Fleeting notes, which are only reminders of information, can be written in any kind of way and will end up in the trash within a day or two.

2. Permanent notes, which will never be thrown away and contain the necessary information in a permanently understandable way. They are always stored in the same way in the same place, either as literature notes in the reference system or written as if for print, in the slip-box.

3. Project notes, which are only relevant to one particular project. They are kept within a project-specific folder and can be discarded or archived after the project is finished. Only if the notes of these three categories are kept separated will it be possible to build a critical mass of ideas within the slip-box.

It is also clear that having good notes is not just about storing them in the slip-box: there must also be an active dialogue with its content. As a starting point, a probing inquiry into the "why?" of having underlined a particular passage, or taken a particular note opens up many avenues for further exploration. An example of this process follows, from Ahrens himself.

The first choice for further inquiry is the slip-box. Maybe there is already something on social inequality that helps me to answer these questions, or at least an indication of where to look. By skimming through the slip-box, I might discover that these ideas could also be helpful for another topic I haven’t thought about. One example is the question of personal responsibility, which is discussed on the example of obesity and the influence of hormones as a sub-topic to a philosophical discussion on free will.

None of it needs to be discussed right away, especially as most of these ideas would require more research and reading. But there is also no reason not to write down these possible connections and come back to them later, if my research points me back to them. The more notes the slip-box contains, the more interesting and prolific this step will become and the more research questions will be triggered.

Just by writing down these questions and making possible connections explicit in writing are the concepts and theories being investigated. Their limitations become as visible as their particular angle on a problem.

a brief explanation of the slip-box and its routine

At the heart of the method lies the slip-box: a physical or digital container for notes that rewards mindful insertion of ideas with organic, spontaneous and novel connections among the material. The insertion is, itself, part of the exercise of composition — the ideas start assembling at the very first interaction with the slip-box.

Make permanent notes. Now turn to your slip-box.

Go through the notes you made in step one or two (ideally once a day and before you forget what you meant) and think about how they relate to what is relevant for your own research, thinking or interests. This can soon be done by looking into the slip-box – it only contains what interests you anyway.

The idea is not to collect, but to develop ideas, arguments and discussions. Does the new information contradict, correct, support or add to what you already have (in the slip-box or on your mind)? Can you combine ideas to generate something new? What questions are triggered by them?

Write exactly one note for each idea and write as if you were writing for someone else: Use full sentences, disclose your sources, make references and try to be as precise, clear and brief as possible.

learning is the endgoal

These practices of note retrieving and archiving — or, more broadly, the interaction with the slip-box — can well constitute an act of learning. Ahrens calls out five mechanisms to define learning: elaboration, spacing, variation, contextual interference and retrieval.

We learn something not only when we connect it to prior knowledge and try to understand its broader implications (elaboration),

but also when we try to retrieve it at different times (spacing)

in different contexts (variation),

ideally with the help of chance (contextual interference)

and with a deliberate effort (retrieval).

All of these processes can be triggered by proper interaction with the slip-box, and the insertion of permanent notes is paramount in encompassing all of these. There are a few guidelines for active practices of elaboration and notes on the strength of elaboration in the process of learning, with a more concrete example on why elaboration works.

the slip-box's free-from as an aid in restructuring arguments

Interacting with the slip-box should help not only in understanding an idea, but also avoiding the common pitfalls of cognitive bias. Tying to his opinions on the shortcomings of some academic writing, Ahrens suggests not committing to a particular thesis or end-goal during the process of writing; instead, one should develop arguments and ideas bottom-up instead of top-down, while using the free-form structure of the slip-box to create a mutable index and structure for an argument. This is one possible way to avoid (cognitive) bias in the structuring of the project.

Experienced academic readers usually read a text with questions in mind and try to relate it to other possible approaches, while inexperienced readers tend to adopt the question of a text and the frames of the argument and take it as a given. What good readers can do is spot the limitations of a particular approach and see what is not mentioned in the text.

further adjacent ideas on personal growth, productivity, etc.

Throughout the book, one finds passages about the nature of self-control and willpower (and how the later supersedes raw intelligence as a predictor for success of the good students — and possibly as a gateway into happiness in general), but also of ego depletion. These are also highly linked to the well-known phenomena of burn-outs, for example.

It is then important to choose a suitable medium for the slip-box (I use Tiddlywiki, but choices abound): there must be a clear, unambiguous procedure to create and store notes. When such a procedure is effortlessy summoned on daily work, even will-power will not suffer so big challenges to keep the motivation for work afloat. There are various intersections with adjacent literature on personal productivity: Flow is mentioned about Zettelkasten as the ideal good structure, and there is praise for David Allen's Get Things Done, which doubles as a very succint and accomplished summary of the method.

Later on, some ideas on learning are later tied to Dweck's work on the growth mindset, on the importance of not being afraid of failure or misdirection. Getting feedback is very important — even, and maybe especially!, if the feedback is negative; even the process of active recall should regularly entail some failing (some of these ideas have also been tackled by Huberman in one of the recent podcasts on learning).