How to Take Smart Notes
Writing and thinking — Sönke Ahrens on Niklas Luhmann's slip-box: how one sociologist turned index cards into 58 books, and how to copy the system.
Mechanisms
Number the notes, not the topics
Luhmann filed each new note directly behind the note it answered, so 22 became 22a and then 22a1.
"The trick is that he did not organise his notes by topic, but in the rather abstract way of giving them fixed numbers. The numbers bore no meaning and were only there to identify each note permanently."
Why it matters
Luhmann filed each new note directly behind the note it answered, so 22 became 22a and then 22a1. A topic folder forces you to decide in advance what an idea belongs to. A fixed number lets an idea grow wherever it connects.
Use when: Your files or notes are sorted into categories that no longer match how you actually think about the work.
Pick the topic from what has already piled up
A topic chosen by brainstorming starts with nothing behind it.
"Do not brainstorm for a topic. Look into the slip-box instead to see where chains of notes have developed and ideas have been built up to clusters."
Why it matters
A topic chosen by brainstorming starts with nothing behind it. A cluster of notes shows where your interest and material already are, so the project starts half-researched.
Use when: You need to choose your next project, essay or product idea and are staring at a blank page.
Index by when you'll want it back
Ahrens's example is a Tversky and Kahneman finding.
"The archivist asks: Which keyword is the most fitting? A writer asks: In which circumstances will I want to stumble upon this note, even if I forget about it?"
Why it matters
Ahrens's example is a Tversky and Kahneman finding. An archivist tags it "psychology." An economist tags it "capital allocation problems," which ties it to questions already on the table and gets it found again.
Use when: You're tagging files, research or bookmarks and the tags describe the item instead of the use.
Hunt for the two ideas you believe that can't both be true
Laying notes next to each other surfaces contradictions that stay hidden when each idea lives in its own context.
"When we realise that we used to accept two contradicting ideas as equally true, we know that we have a problem – and problems are good because we now have something to solve."
Why it matters
Laying notes next to each other surfaces contradictions that stay hidden when each idea lives in its own context. Ahrens cites Albert Rothenberg's finding that building oppositions is a reliable way to produce new ideas.
Use when: Your thinking on a subject feels settled and you want to find where it is weak.
Tie yourself to the mast with the workflow
Odysseus didn't rely on willpower against the Sirens.
"With a good system, the mere necessities of the workflow will force us to act more virtuously without actually having to become more virtuous."
Why it matters
Odysseus didn't rely on willpower against the Sirens. Ahrens applies the same move to confirmation bias: if the system has you collect every relevant note regardless of which side it supports, good habits come from the process.
Use when: You keep resolving to be more disciplined and want to design the process so discipline isn't required.
Pretend it's just notes for yourself
Slavoj Žižek said this in an interview about how he starts.
"…he wouldn’t be able to write a single sentence if he didn’t start by convincing himself he was only writing down some ideas for himself, and that maybe he could turn it into something publishable later."
Why it matters
Slavoj Žižek said this in an interview about how he starts. Lowering the stakes in your own head gets the words moving. By the time he stopped, the only thing left was revising the draft he already had.
Use when: The importance of a piece of writing is keeping you from starting it.
Cut to a second file you'll never open
Deleting a good passage feels like a loss, so people keep material that has no job in the argument.
"For every document I write, I have another called “xy-rest.doc,” and every single time I cut something, I copy it into the other document, convincing myself that I will later look through it and add it back where it might fit. Of course, it never happens – but it still works."
Why it matters
Deleting a good passage feels like a loss, so people keep material that has no job in the argument. Moving it to a holding file removes the loss and the passage disappears from the draft. Ahrens notes Richard Thaler does the same.
Use when: A draft, deck or product is bloated with pieces you can't bring yourself to cut.
Arguments
Brainstorming is a memory test in disguise
Ahrens opens his case against brainstorming with Munger's line.
"Remember the lesson: ‘An idea or a fact is not worth more merely because it is easily available to you.’"
Why it matters
Ahrens opens his case against brainstorming with Munger's line. What comes to mind in a session is what is most recent or vivid, which is a poor proxy for what is most promising. An external store of notes widens the pool.
Use when: A team is about to pick a direction from whatever ideas surface in a single meeting.
Separate writing from proofreading
Finding words needs loose, floating attention.
"We tend to call extremely slow writers, who always try to write as if for print, perfectionists." "A real professional would wait until it was time for proofreading, so he or she can focus on one thing at a time."
Why it matters
Finding words needs loose, floating attention. Correcting them needs narrow, focused attention. Trying to do both in the same pass stalls the work, which is what gets mislabeled as perfectionism.
Use when: You or someone on your team edits every sentence while drafting and the draft barely moves.
Keep the outline movable until the end
Ahrens keeps a separate outline for each project and expects it to change until late.
"The structure of an argument is part of it and therefore will change during the process of developing it – it is not a vessel to be filled with content."
Why it matters
Ahrens keeps a separate outline for each project and expects it to change until late. Once it stops changing much, he calls it a table of contents, and chapters can still move at the very end.
Use when: You've locked a plan or outline early and the material keeps fighting it.
External rewards don't build a loop
Ahrens argues motivation only sustains itself when the work produces its own visible progress.
"Any attempts to trick ourselves into work with external rewards (like doing something nice after finishing a chapter) are only short-term solutions with no prospect of establishing a positive feedback loop."
Why it matters
Ahrens argues motivation only sustains itself when the work produces its own visible progress. A slip-box gives that feedback every day, as notes pile up and connect.
Use when: You're relying on treats or bonuses to keep yourself or a team going on long work.
The brain jumps to conclusions, paper doesn't
Ahrens pairs this with Kahneman's description of the brain as "a machine for jumping to conclusions." Writing an argument out makes its gaps visible in a way that thinking it through in your head does not.
"Luhmann states as clearly as possible: it is not possible to think systematically without writing (Luhmann 1992, 53)."
Why it matters
Ahrens pairs this with Kahneman's description of the brain as "a machine for jumping to conclusions." Writing an argument out makes its gaps visible in a way that thinking it through in your head does not.
Use when: You're about to make a decision you've only reasoned through in your head.
Concepts
Rereading feels like learning
Familiarity produces the sensation of knowing without the substance.
"Rereading is especially dangerous because of the mere-exposure effect: The moment we become familiar with something, we start believing we also understand it."
Why it matters
Familiarity produces the sensation of knowing without the substance. Ahrens recommends testing yourself and writing the idea out in your own words, both harder and both more accurate signals of what you've learned.
Use when: You're preparing for a test, a pitch or a board meeting by going over the same material again.
Evidence
Write it down and the brain lets go
Bluma Zeigarnik saw a waiter recall unpaid orders perfectly and forget them once paid.
"Open tasks tend to occupy our short-term memory – until they are done." "All we have to do is to write them down in a way that convinces us that it will be taken care of."
Why it matters
Bluma Zeigarnik saw a waiter recall unpaid orders perfectly and forget them once paid. Her follow-up research showed that writing a task down in a trusted place frees the mind about as well as finishing it.
Use when: Unfinished tasks keep pulling at your attention while you try to focus on one thing.
Handwriting forces you to translate
In Mueller and Oppenheimer's study, students who took notes on laptops wrote more but understood less.
"Handwriting makes pure copying impossible, but instead facilitates the translation of what is said (or written) into one’s own words."
Why it matters
In Mueller and Oppenheimer's study, students who took notes on laptops wrote more but understood less. Slower handwriting forced them to choose and rephrase, and that processing is where the understanding happened.
Use when: You take long notes in meetings or lectures and remember little of what was said.
The slip-box got him a professorship in a year
Luhmann was a civil servant without a doctorate when Helmut Schelsky urged him toward a professorship, which normally meant years of degrees.
"He turned to his slip-box, and with its help he obtained all requirements in less than a year."
Why it matters
Luhmann was a civil servant without a doctorate when Helmut Schelsky urged him toward a professorship, which normally meant years of degrees. Because his notes were already a body of work, he could write the dissertation and habilitation quickly.
Use when: A big opportunity opens and you need to show finished work fast.
Passages
Do only what is easy
Luhmann's statement sounds lazy until you see the system behind it.
"I only do what is easy. I only write when I immediately know how to do it. If I falter for a moment, I put the matter aside and do something else."
Why it matters
Luhmann's statement sounds lazy until you see the system behind it. With dozens of open threads in the slip-box, there was always another task he knew how to do, so getting stuck on one never stopped the work.
Use when: You're grinding on one blocked task and could be moving another forward.
Rules
One idea per note, one screen per note
Luhmann used A6 slips.
"By restricting ourselves to one format, we also restrict ourselves to just one idea per note and force ourselves to be as precise and brief as possible." "A good rule of thumb for working digitally is: Each note should fit onto the screen and there should be no need of scrolling."
Why it matters
Luhmann used A6 slips. The size limit made every note a single unit that could be moved and recombined with others later. A note holding three ideas can only ever sit in one place.
Use when: You're building a library of ideas, research or reusable material and want the pieces to combine later.
Write every note for a stranger
The stranger is your future self, who will have forgotten the context within weeks.
"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."
Why it matters
The stranger is your future self, who will have forgotten the context within weeks. Notes written in full sentences can be dropped straight into a draft. Keyword scraps have to be rethought from scratch.
Use when: You're capturing anything you expect to use in writing, a pitch or a decision months from now.
Everything lands in one inbox, cleared within a day
Ahrens treats quick jottings as reminders of a thought, too thin to hold the thought itself.
"If you use other tools, make sure everything ends up in one place, a central inbox or something like that, where you can process it soon, ideally within a day."
Why it matters
Ahrens treats quick jottings as reminders of a thought, too thin to hold the thought itself. They go stale fast. One collection point and a one-day deadline turn them into proper notes or into trash before you forget what they meant.
Use when: Your ideas are scattered across apps, notebooks and voice memos and you can't find any of them.
Darwin's golden rule: write down the objection at once
Memory filters out what contradicts us.
"…whenever a published fact, a new observation or thought came across me, which was opposed to my general results, to make a memorandum of it without fail and at once; for I had found by experience that such facts and thoughts were far more apt to escape from the memory than favorable ones."
Why it matters
Memory filters out what contradicts us. Darwin countered it by recording disconfirming facts immediately, and wrote that as a result very few objections were raised against his views that he hadn't already noticed and tried to answer.
Use when: You're building a case for a plan or a thesis and want the objections in hand before anyone else raises them.
The introductory lecture test
Ahrens calls reading with a pen in hand the small-scale version of that lecture.
"Physicist and Nobel Prize winner Richard Feynman once said that he could only determine whether he understood something if he could give an introductory lecture on it."
Why it matters
Ahrens calls reading with a pen in hand the small-scale version of that lecture. A note written for someone who lacks your context exposes the gaps that rereading hides.
Use when: You think you understand a subject well enough to explain it, sell it or decide on it.
Rephrase the quote before you file it
Copying a passage feels productive and defers the thinking.
"Be extra selective with quotes – don’t copy them to skip the step of really understanding what they mean."
Why it matters
Copying a passage feels productive and defers the thinking. Restating it in your own words forces the understanding at the moment you have the source open.
Use when: Your research files are full of highlighted passages you couldn't explain without rereading them.
Connections
Compound interest versus a piggy bank
Trollope wrote 250 words every 15 minutes before work, and the pages added up linearly.
"But the main reason is the slip-box, which compares to Trollope’s technique as investing with compounded interest compares to a piggy-bank."
Why it matters
Trollope wrote 250 words every 15 minutes before work, and the pages added up linearly. Luhmann's notes linked to each other, so each new note made the old ones more useful. He published 58 books and hundreds of articles.
Use when: You're choosing between a daily output quota and a system where past work feeds future work.
Simple boxes beat optimal packing
Experienced stevedores could pack a hold better than any standard container.
"Most ship owners had in fact considered the idea of putting different kinds of products into the same sized boxes as fairly abstruse."
Why it matters
Experienced stevedores could pack a hold better than any standard container. Malcom McLean's container won anyway, because standardizing the unit made every step around it faster and cheaper. Ahrens argues standard notes work the same way.
Use when: Experts defend a custom process that performs well at one step and slows down the whole chain.