Sönke Ahrens' How to Take Smart Notes: Modern Systematization of the Zettelkasten Method

Published:
  Lastmod: 2025-10-27
Knowledge Management
by Ernest Chiang

Post Title Image (Hand-drawn by Ernest Chiang. You might also be interested in his Ernest PKM workflow.)

1️⃣ Introduction: Making Zettelkasten Learnable and Replicable

In 2017, German scholar Sönke Ahrens published a book that transformed the knowledge management field: How to Take Smart Notes. 1

This book accomplished something important: systematizing, proceduralizing, and making actionable Niklas Luhmann's Zettelkasten method.

Before Ahrens, Zettelkasten was more like a “legend”—we knew Luhmann wrote 70 books using this method, but weren’t quite clear how ordinary people could replicate this system. Luhmann’s own 1981 paper “Communicating with Slip Boxes” was more philosophical reflection than operational manual. (I personally prefer reflection, but many friends have been asking about methods, so I compiled this note.)

“Writing is not what happens after thinking.
Writing is the medium of thinking."

— Sönke Ahrens, How to Take Smart Notes (2017)

Ahrens attempted to:

  • Abstract Luhmann’s practice into replicable steps
  • Add support from modern learning science and cognitive psychology
  • Propose clear classification of three note types
  • Provide practical advice for the digital age

But this also brought a problem: many people mistook Ahrens’ interpretation for Luhmann’s original method.

This article explores Ahrens’ contributions, innovations, and the differences between Ahrens and Luhmann’s original method.

📖
Further Reading

Niklas Luhmann’s Original Zettelkasten:
Two Slip Boxes, Fixed Numbering, and Communication Partner

2️⃣ Sönke Ahrens’ Core Interpretation: Three Note Types

Ahrens’ most important contribution was classifying notes into three distinct types. This framework made the Zettelkasten method learnable. 2

%%{init: {'theme':'default'}}%%
graph TB
    %% Input and Sources
    Reading[Reading/Observation/Conversation]:::source

    %% Note Types - Instances in Blue/Orange
    Fleeting[Fleeting Notes • Quick capture • Temporary • Process within days]:::fleeting
    Literature[Literature Notes • Extremely concise • With bibliographic info • Own language]:::literature
    Permanent[Permanent Notes • Self-contained • Permanent storage • Linkable]:::permanent
    Project[Project Notes • Project-specific • Temporary • Separately managed]:::project

    %% Main Knowledge Base
    Zettelkasten[Zettelkasten Main Slip Box]:::mainbox

    %% Outputs
    Writing[Writing Output: Articles/Papers/Books]:::output

    %% Connections
    Reading -->|Quick notes| Fleeting
    Reading -->|Reading summary| Literature

    Fleeting -->|Daily processing: Transform| Permanent
    Literature -->|Deep thinking: Rewrite| Permanent

    Permanent -->|Store| Zettelkasten
    Zettelkasten -->|Link & evolve| Zettelkasten

    Zettelkasten -->|Collect related cards| Project
    Project -->|Organize into writing| Writing

    %% Styling
    classDef source fill:#E8E8E8,stroke:#999,stroke-width:2px,color:#000
    classDef fleeting fill:#FFE6CC,stroke:#FF9900,stroke-width:2px,color:#000
    classDef literature fill:#CCE5FF,stroke:#0066CC,stroke-width:2px,color:#000
    classDef permanent fill:#0080FF,stroke:#0060CC,stroke-width:3px,color:#FFF
    classDef project fill:#D9EAD3,stroke:#6AA84F,stroke-width:2px,color:#000
    classDef mainbox fill:#FF8000,stroke:#CC6600,stroke-width:3px,color:#000
    classDef output fill:#F4CCCC,stroke:#CC0000,stroke-width:2px,color:#000

2.1 Fleeting Notes

  • Definition
    • Quick-capture temporary notes recording any input or idea.
  • Characteristics
    • Very temporary: designed to be discarded
    • Casual, informal: don’t need complete sentences or structure
    • Reminder function: just need to help you recall the thought at the time
    • Must be processed within days: otherwise they lose meaning
  • Ahrens particularly emphasizes the habit of “reading with a pen.” He believes if you read without taking fleeting notes, you’re not truly using his method (Ahrens, 146). 2
  • Relationship to Luhmann:
    • ❌ No relationship.
    • This is a category Ahrens independently emphasized. Luhmann probably also recorded temporary thoughts, but in his remaining cards, he didn’t systematize it as an independent note type. 2
Ernest PKM Workflow:
  • I use multiple tools to capture Fleeting Notes:
    • iPhone Notes.app
      • Fastest capture tool.
      • While walking, in meetings, sudden inspirations.
      • Uses iCloud to sync across all Apple devices.
      • Have one pinned note named “Thoughts Stream.”
    • Paper and pen
      • During certain deep thinking moments.
      • Meetings, coffee shops, on planes.
      • reMarkable Paper Pro, Field Notes, or iPad + Apple Pencil (current frequency order in 2025).
      • Take photos into iPhone album.
    • Todoist / ClickUp
      • If it’s an idea with a direct action plan, put into corresponding area’s to-do items.
      • Personal matters default to Todoist.
      • Work matters default to ClickUp.
  • Processing frequency
    • Process during morning routine time each day (as much as possible).
    • Processing means execute, archive, or leave it.
  • Retention period
    • Should regularly delete in theory, but in practice I mostly just leave them.

2.2 Literature Notes

  • Definition
    • Notes taken on source content while reading, including bibliographic information and brief summaries.
  • Characteristics
    • Extremely concise, not verbatim excerpts but highly condensed key points
    • In your own language, rewrite, not copy-paste
    • With bibliographic information: author, title, page numbers, etc.
    • Stored in bibliographic system, separate from main slip box
  • How to create 1
    • While reading, write in literature notes:
      • Page x has this concept
      • Page y has that argument
    • Keep extremely concise and highly selective
    • Only record content you think you might use in the future
    • Use your own language, not original quotes
  • Relationship to Luhmann:
    • ✅ Related
    • This corresponds to Luhmann’s Bibliographic Slip-Box. But Ahrens systematized it and clearly indicated this is an independent step.
Ernest PKM Workflow:
  • For Literature Notes, my approach is to record thoughts in notes when highlighting.
    • This way, regardless of device or app, everything can be collected into Heptabase Highlights through Readwise.
  • Source integration:
    • Kindle highlights and notes → Automatically import to Readwise
    • Safari Books highlights and notes → Automatically import to Readwise
    • Kobo highlights and notes → Automatically import to Readwise
    • Readwise Reader highlights → Native in Readwise
    • Physical books, paper notes, reMarkable Paper Pro → Manually input to Heptabase (rarely happens)
  • Summary principles:
    • Not copying original text, but re-describing in own words
    • When highlighting, try to add current thoughts in notes, or practice paraphrasing, or add own context scenarios
    • Only record core concepts that “might be useful” (you don’t want to type too much with Kindle’s phonetic input… though as an introvert, I speak few words normally but type many words XDD)
    • Preserve bibliographic information and page numbers for backtracking
  • Tag system:
    • Increasingly not maintaining tags, only maintain tags for specifically focused topics.
    • Convenient for later batch processing related topics in Heptabase.
  • Literature Notes aren't "collection," but "selection and filtering".

2.3 Permanent Notes

  • Definition:
    • Well-considered, complete thoughts expressed in your own language, permanently stored in the main slip box.
  • Characteristics:
    • Never discard: designed for permanent storage
      • (Usually only have time to add new notes, rarely have time to delete notes.)
      • (Rather think of it as: this permanent note is in a state of “already organized by myself, for my future self, ready to use anytime.” That’s how I see it.)
    • Understandable without context
    • In your own language
    • One card contains only one idea
    • Designed to link with other cards
  • How to create: 1
    • Review fleeting notes and literature notes weekly (monthly, or some cycle)
    • Think about the relationship of these ideas to your research, interests, thinking
    • Choose ideas worth keeping
    • Rewrite as independent, complete, clear cards
    • Decide card’s position in system, establish connections
    • Discard fleeting notes and literature notes (or move to Archived, if you also use PARA)
  • Relationship to Luhmann:
    • ✅ Related
    • This corresponds to Luhmann’s Main Slip-Box. This is the closest part between the two.
Ernest PKM Workflow:
  • My Permanent Notes are currently mainly stored in Heptabase
    • If need to share with team or friends, use whiteboard sharing function.
    • For work-related Permanent Notes, I write some in weekly reports.
      • (But this violates the principle of one idea per card, but I can’t find another more suitable place, I want a place where both I and colleagues will pass by and see.)
  • From Readwise to Heptabase workflow:
    • Readwise automatically syncs to Heptabase “Highlights” tab anytime
    • I browse these imported highlights in Heptabase Highlights tab
    • Edit highlights that don’t have Notes yet
    • Put on some Whiteboard, sometimes recreate cards
  • Connection strategy:
    • Visually arrange cards on Heptabase whiteboard
    • Place related cards on same whiteboard
    • Use arrows and tags to establish relationships
    • Regularly reorganize whiteboard structure
  • Quality control:
    • One card contains only one idea
    • Content should be understandable to future self (not dependent on memory)
    • Can be read independently (author says doesn’t need context) (but since I put them in whiteboards, when I review, there is context)

3️⃣ What Did Ahrens Add?

Besides systematizing Luhmann’s method, Ahrens also added some new elements.

3.1 Project Notes

  • Definition:
    • Notes related to specific external projects, such as paper outlines, presentation points, project to-do items.
  • Characteristics:
    • Only meaningful for single project
    • Temporary, can be discarded or archived after project ends
    • Don’t enter main slip box, separate from permanent notes
  • Why important:
    • This solves a practical problem—many people mix “drafts for writing papers” with “permanent knowledge notes.” Ahrens clearly separates these two.
  • Relationship to Luhmann:
    • ❌ No relationship.
    • This is a new category Ahrens added himself. 2 Luhmann might have had similar things, but didn’t explicitly distinguish them.

3.2 Emphasis on “Reading with a Pen” Habit

  • Ahrens strongly emphasizes must use pen to record (fleeting notes) while reading.
  • His argument:
    • Brain isn’t good at memory, good at thinking
    • If you don’t write down thoughts while reading, you’ll forget
    • This habit forces you to “actively read”
  • This emphasis is Ahrens’ characteristic; Luhmann didn’t particularly emphasize this (though in Luhmann’s era they could only use pen?!)

3.3 Digital Tool Recommendations

  • Ahrens wrote in an era (2017) when digital note tools had matured. He proposed some tool recommendations:
    • Bibliographic management: use Zotero as “digital bibliographic slip box”
    • Main slip box: can use any tool supporting bidirectional links (were there many in 2017?! I remember most note-taking software only started supporting Backlinks after 2022, before that mostly manual processing.)
    • Key point: tools should support Zettelkasten’s core principles (connection, search, expansion)
  • This obviously didn’t exist in Luhmann’s era.

4️⃣ Comparison with Luhmann’s Original Method

AspectLuhmann’s Original MethodAhrens’ Interpretation
Note ClassificationTwo slip boxes (bibliographic + main)Three note types (fleeting + literature + permanent) + project notes
Fleeting Notes❌ Not explicitly systematized1️⃣ Independent first step, emphasizes must use pen to record
Literature Notes1️⃣ Bibliographic slip box2️⃣ Systematized as independent step, emphasizes conciseness and rewriting
Permanent Notes2️⃣ Main slip box3️⃣ Same concept, but more explicit creation process
WorkflowReading → bibliographic cards → thinking → permanent cardsReading + fleeting notes → literature notes → permanent notes
Numbering SystemFolgezettel (1, 1a, 1a1)Optional, not mandatory (digital tools can use links instead)
Connection StrategyCross-references, hub notes, structure notesSame, but emphasizes bidirectional links more
Philosophical DepthSystems theory, communication partner, order and chaosLearning science, cognitive psychology, writing process
Target AudienceAcademic researchers (himself)Students, scholars, nonfiction writers

5️⃣ Further Reading and References

Ahrens’ Work

  • “From Fleeting Notes to Project Notes – Concepts of Sönke Ahrens Explained,” zettelkasten.de

Further Reading

Epilogue

Sönke Ahrens’ contribution was perhaps transforming Zettelkasten from “academic legend” to “learnable method.” Without his book, I might not have had the chance to learn about Niklas Luhmann’s Zettelkasten.

Worth mentioning: you don’t need to demand “perfectly executing Ahrens’ steps” from yourself. I must reiterate the importance of “comfort” mentioned in Ernest PKM. You need to feel comfortable for your knowledge system to have a chance of continuing:

  • Continuous thinking
  • Building connections
  • Generating insights
  • Completing works

If Ahrens’ three-part classification helps you, try it and adjust to what feels comfortable for you.

If Luhmann’s philosophical depth inspires you more, try it. If you want to mix both and create your own version, that’s also good.

The core is always: use writing to think, let the knowledge system you design dialogue with yourself.

This is what Luhmann and Ahrens both want to tell us (I think).

If you have articles on your website about understanding and practicing Ahrens’ How to Take Smart Notes, feel free to leave a message to Ernest to exchange links. Or let’s discuss together on Threads | Twitter/X.

  1. Ahrens, Sönke (2017). How to Take Smart Notes: One Simple Technique to Boost Writing, Learning and Thinking – for Students, Academics and Nonfiction Book Writers. CreateSpace Independent Publishing Platform. ↩︎ ↩︎ ↩︎

  2. “From Fleeting Notes to Project Notes – Concepts of Sönke Ahrens Explained,” zettelkasten.de ↩︎ ↩︎ ↩︎ ↩︎