I've always appreciated this serendipity, but never read a source talking about it specifically.

Some interesting shade here, but he's probably right with respect to the additional work involved in a personal collection which isn't shared at scale.

The real work is the indexing of the material within the books, the assigned numbers are just a means of finding them.

https://www.librarything.com/mds

Melvil Decimal System (LibraryThing's equivalent of DDC, apparently in an attempt not to run afoul of the OCLC's Trademark.)

https://blog.librarything.com/2016/07/introducing-dewmojis/

I've sketched it out elsewhere but let's memorialize the broad strokes here because we're inspired at the moment... come back later and add in quotes from Luhmann and other sources (@Heyde1931).

Luhmann was balancing the differences between topically arranged commonplaces and the topical nature of the Dewey Decimal System (a standardized version across thousands of collections) and building neighborhoods of related ideas.

One of the issues with commonplace books, is planning them out in advance. How might you split up a notebook for long term use to create easy categories when you don't know how much room to give each in advance? (If you don't believe me, stop by r/commonplacebooks where you're likely to see this question pop up several times this year.) This issue is remedied when John Locke suggests keeping commonplaces in chronological order of their appearance and cross-indexing them.

This creates a new problem of a lot of indexing and increased searching over time as the commonplace book scales. Translating to index cards complicates things because they're unattached and can potentially move about, so they don't have the anchor effectuated by their being bound up in a notebook. But being on slips allows them to be more easily shuffled, rearranged, and even put into outlines, which are all fantastic affordances when looking for creativity or scaffolding things out into an article or book for creation.

As a result, numbering slips creates a solid anchor by which the cards can be placed and always returned for later finding and use. But how should we number them? Should it be with integers and done chronologically? (1, 2, 3, ..., n) This is nice, but makes a mish-mash of things and doesn't assist much in indexing or finding.

Why not go back to Dewey, which has been so popular? But not Dewey in the broadest sense of using numbers to tie ideas to concrete categories. An individual's notes are idiosyncratic and it would be increasingly rare for people to have the same note, much less need a standardized number for it (and if they were standardized, who does that work and how is it distributed so everyone could use it?) No, instead, let's just borrow the decimal structure of Dewey's system. One of the benefits of his decimal structure is that an infinity of new books can be placed on ever-expanding bookshelves without needing to restructure the numbering system. Just keep adding decimal places onto the end when necessary. This allows for immense density when necessary. But, importantly, it also provides some fantastic level of serendipity.

Let's say you go to learn about geometry, so you look up the topic in your trusty library card catalog. Do you really need to look at the hundreds of records returned? Probably not. You only need the the Dewey Decimal Number 516. Once you're at the shelves, you can browse through that section to see what's there and interesting in the space. You might also find things on the shelves above or below 516 and find the delights of topology and number theory or abstract algebra and real analysis. Subjects you might not necessarily have had in mind will suddenly present themselves for your consideration. Even if your initial interest may have been in Zhongmin Shen's Lectures on Finsler geometry (516.375), you might also profitably walk away with James E. Humphreys' Introduction to Lie Algebras and Representation Theory (512.55).

So what happens if we use these decimal numbers for our notes? First we will have the ability to file things between and amongst each other to infinity. By filing things closest to things which seem related to each other, we'll create neighborhoods of ideas which can easily grow over time. Related ideas will stay together while seemingly related ideas on first blush may slowly grow away from each other over time as even more closely related ideas move into the neighborhood between them. With time and careful work, you'll have not only a breadth of ideas, but a massive depth of them too.

The use of decimal numbering provides us with a few additional affordances:

1 (Neighborhoods of ideas) 1.1 combinatorial creativity Neighborhoods of ideas can help to fuel combinatorial creativity and forge new connections as well as insight over time. 1.2 writing One might take advantage of these growing neighborhoods to create new things. Perhaps you've been working for a while and you see you have a large number of cards in a particular area. You can, to some extent, put your hand into your box and grab a tranche of notes. By force of filing, these notes are going to be reasonably related, which means you should be able to use them to write a blog post, an article, a magazine piece, a chapter, or even an entire book (which may require a few fistfuls, as necessary.)

2 (Sparse indexing) We don't need to index each and every single topic or concept into our index. Because we've filed things nearby, if a new card about Finsler geometry relates to another and we've already indexed the first under that topic, then we don't need to index the second, because our future selves can easily rely on the fact that if we're interested in Finsler geometry in the future, we can look that up in the index, and go to that number where we're likely to see other cards related to the topic as well as additional serendipitous ideas related to them in that same neighborhood.

You may have heard that as Luhmann progressed on his decades long project, broadly on society and within the area of sociology, he managed to amass 90,000 index cards. How many do you suppose he indexed under the topic of sociology? Certainly he had 10s of thousands relating to his favorite subject, no? Of course he did, but what would happen over time as a collection grows? Having 20,000 indexed entries about sociology doesn't scale well for your search needs. Even 10 indexed entries may be a bit overwhelming as once you find a top level card, hundreds to thousands around it are going to be related. 10 x 100 = 1,000 cards to flip through. So if you're indexing, be conservative. In the roughly 45 years of creating 90,000 slips, Luhmann only indexed two cards with the topic of "sociology". If you look through his index, you'll find that most of his topical entries only have pointers to one or two cards, which provide an entryway into those topics which are backed up with dozens to hundreds of cards on related topics. In rarer, instances you might find three or four, but it's incredibly rare to find more than that.

Over time, one will find that, for the topics one is most interested in, the number of ideas and cards will grown without bound. Here it makes sense to use more and more specific topics (tags, categories, taxonomies) all of which are each also sparsely indexed. Ultimately one finds that in the limit, the categories get so fractionalized that the closest category one idea has with another is the fact that they're juxtaposed closely by number. The of the decimal expansion might say something about the depth or breadth of the relationship between ideas.

Something else arises here. At first one may have the tendency to associate their numbers with topical categories. This is only natural as it's a function at which humans all excel. But are those numbers really categories after a few weeks? Probably not. Treat them only as address numbers or GPS coordinates to be able to find your way. Your sociology section may quickly find itself with invasive species of ideas from anthropology and archaeology as well as history. If you treat all your ideas only at the topical level, they'll be miles away from where you need them to be as the smallest level atomic ideas collide with each other to generate new ideas for you. Naturally you can place them further away if you wish and attempt to bridge the distance with links to numbers in other locations, but I suspect you'll find this becomes pretty tedious over time and antithetical when it comes time to pull out a handful and write something. It's fantastically easier to pull out a several dozen and begin than it is to go through and need to pull out linked cards in a onesy-twosies manner or double check with your index to make sure you've gotten the most interesting bits. This becomes even more important as your collection scales.

This analogy is kind of hilarious from the perspective of Luhmann's Zettelkasten.

reply to oxytonic on 2023-01-08 at https://hypothes.is/a/8QdgetQOEe2XG6u5i9iAHQ

In my experience, alternating alphanumeric codes give you the "gist" of the original context. Purely with reference to my rough outline, my notecard "3516/b" implies psychology (3XXX), cognition (35XX), and memory (351X). Even the single slash implies a level of abstraction and/or specificity.

But it's not enough because it runs the risk of locking you in. Forward links on the card (or forward links to the card!) offer comparable if not competitive recontextualization, which is most likely what Luhmann means by "multiple storage".

Caution: My note here has some significant missing context which results from significant additional research.

The primary issue with analog slip boxes, particularly in academic research of Luhmann's day, was one of multiple storage. No one else I'm aware of prior to his time used Luhmann's filing scheme (and very few after until about 2013). Instead most filed multiple copies of their notes under category headings like "psychology", "cognition", and "memory" (to use your example) so that those ideas would be readily available when they came to work on their ideas relating to cognition, for example. This involved a tremendous amount of copying work. (For reference, see Heyde, Johannes Erich. Technik des wissenschaftlichen Arbeitens: zeitgemässe Mittel und Verfahrungsweisen. Junker und Dünnhaupt, 1931. which is the handbook which Luhmann used to scaffold his method.) It was this copying and filing under multiple categories which was commonly referred to as multiple storage. Many academics got around it by hiring assistants or secretaries who would do this duplicative work and filing on their behalf; Luhmann didn't have this additional help and it may have been a portion of the pressure for the evolution of his method.

Instead Luhmann used branching and cross-indexing his ideas along with regular use and familiarity of the space within his boxes. While his zettelkasten may seem on the surface to be done by category, the way you suggest, it definitely is not. Some of this appearance is suggested by editorial decisions made by the curators of his digital archive and, in larger part, by Scott Scheper who (sadly in my opinion) recommends using the Academic Outline of Disciplines as top level categories a practice which heavily belies some of what Luhmann was doing. While Luhmann was inspired by the Dewey Decimal System, he wasn't using the parts of it that equated numbers with topics, in part because he didn't need to and it would have been counterproductive to his ultimate method—specifically causing him to deal with multiple storage. Modern (digital) database theory and practice allows some note takers an easier way around this problem.

For more on this see: - https://boffosocko.com/2022/10/27/thoughts-on-zettelkasten-numbering-systems/ - https://boffosocko.com/2023/01/19/on-the-interdisciplinarity-of-zettelkasten-card-numbering-topical-headings-and-indices/

reply to u/JeffB1517 at https://www.reddit.com/r/Zettelkasten/comments/16ulsye/comment/k2mb8s2/?utm_source=reddit&utm_medium=web2x&context=3

I've only seen some modest discussion of DDC and outside of Joseph Voros, vanishingly little discussion (much less usage) of Propædia as classification systems for zettelkasten id numbering. I'm wholly unaware of anyone actively using the Universal Decimal Classification, but would love to see examples of it in action if they exist. From where are you drawing your sampling of "lots of people"? Do you use Library of Congress classification for your own, and if so, can you provide an example of numbers and titles of half a dozen cards to demonstrate your specific method? Given the prevalence of its use in filing/ordering, I'd more likely place the ID at the top of the card over the bottom and put other links at the bottom. Is there a particular affordance that would encourage you to do it the opposite?

Perhaps you're including it in the idea of "related notes", but I also keep a separate reference section on each card for the source or related context of the main idea or excerpted quotation.

—Georg Christoph Lichtenberg, Notebook E, #46, 1775–1776

In this single paragraph quote Lichtenberg, using the model of Italian bookkeepers of the 18th century, broadly outlines almost all of the note taking technique suggested by Sönke Ahrens in How to Take Smart Notes. He's got writing down and keeping fleeting notes as well as literature notes. (Keeping academic references would have been commonplace by this time.) He follows up with rewriting and expanding on the original note to create additional "explanations" and even "connections" (links) to create what Ahrens describes as permanent notes or which some would call evergreen notes.

Lichtenberg's version calls for the permanent notes to be "separated and ordered" and while he may have kept them in book format himself, it's easy to see from Konrad Gessner's suggestion at the use of slips centuries before, that one could easily put their permanent notes on index cards ("separated") and then number and index or categorize them ("ordered"). The only serious missing piece of Luhmann's version of a zettelkasten then are the ideas of placing related ideas nearby each other, though the idea of creating connections between notes is immediately adjacent to this, and his numbering system, which was broadly based on the popularity of Melvil Dewey's decimal system.

It may bear noticing that John Locke's indexing system for commonplace books was suggested, originally in French in 1685, and later in English in 1706. Given it's popularity, it's not unlikely that Lichtenberg would have been aware of it.

Given Lichtenberg's very popular waste books were known to have influenced Leo Tolstoy, Albert Einstein, Andre Breton, Friedrich Nietzsche, and Ludwig Wittgenstein. (Reference: Lichtenberg, Georg Christoph (2000). The Waste Books. New York: New York Review Books Classics. ISBN 978-0940322509.) It would not be hard to imagine that Niklas Luhmann would have also been aware of them.

Open questions: <br /> - did Lichtenberg number the entries in his own waste books? This would be early evidence toward the practice of numbering notes for future reference. Based on this text, it's obvious that the editor numbered the translated notes for this edition, were they Lichtenberg's numbering? - Is there evidence that Lichtenberg knew of Locke's indexing system? Did his waste books have an index?

He's cleverly noticed that many books and articles use a decimal outlining scheme already, so why not leverage that here.

reply to drogers8 at https://www.reddit.com/r/antinet/comments/13eyg8p/comment/jkaksn4/?utm_source=reddit&utm_medium=web2x&context=3

You can find some basic top level or second level DDC listings online, but to get the full set of listings, you've got to subscribe to the system which is updated every few years, something only library systems and large publishers typically do. To give yourself an idea of how deep this rabbit hole goes the DDC 23 is four volumes long and each volume is in the 1,000 page range. The DDC 23 self-identifies as 0.25.4'31-dc22. For most categories DDC generally only goes as deep as the thousands place (like Finsler geometry) though others will go slightly deeper usually to designate locations/cities. Most libraries only categorize to the tenths place, and sometimes these numbers can be found on the copyright page of books, often with the DDC volume number. I mentioned the UDC in that piece, but didn't give any links, but you could try:<br /> - https://udcsummary.info/php/index.php?lang=en - https://udcc.org/index.php/site/page?view=subject_coverage - https://en.wikipedia.org/wiki/Universal_Decimal_Classification

Honestly, you're wasting time and making way more work for yourself to adopt one of these numbering methods for a Luhmann-esque zettelkasten. Try asking yourself this question: What benefits/affordances will I get in the long run for having my numbering system mirror the DDC or UDC? (Unless you can come up with a really fantastic answer, you're just making more work to look up headings/numbers on a regular basis.)

In practice the numbers are simply addresses so you can quickly find things again using your index. If you're doing threads of cards (folgezettel), you're going to very quickly have tangentially related ideas of things mixed together anyway. (As an example, I've got lots of science and even some anthropology mixed into my math section, so having DDC numbers on those would be generally useless at the end of the day.) If it helps, Nicolas Gatien has a pretty reasonable and short video which makes this apparent: https://www.youtube.com/watch?v=tdHH3YjOnZE.

reply to u/drogers8 at https://www.reddit.com/r/antinet/comments/13eyg8p/extended_numbering_and_why_use_outline_of/

Based on my research, Scott Scheper was the one of the original source for people adopting the Academic Outline of Disciplines. I've heard him say before that he recommends it only as a potential starting place for people who are new to the space and need it as a crutch to get going. It's an odd suggestion as almost all of the rest of his system is so Luhmann-based. I suspect it's a quirk of how he personally started and once moving it was easier than starting over. He also used his own ZK for showing others, and it's hard to say one thing in a teaching video when showing people something else. Ultimately it's hard to mess up on numbering choices unless you're insistent on using only whole numbers or natural numbers. I generally wouldn't suggest complex numbers either, but you might find some interesting things within your system if you did. More detail: https://boffosocko.com/2022/10/27/thoughts-on-zettelkasten-numbering-systems/ The only reason to have any standardized base or standardized numbers would be if you were attempting to have a large shared ZK with others. If this is your intent, then perhaps look at the Universal Decimal Classification, though a variety of things might also work including Dewey Decimal.

As humans we're good at separating things based on categories. The Dewey Decimal System systematically separates mathematics and history into disparate locations, but your zettelkasten shouldn't force this by overthinking categories. Perhaps the overlap of math and history is exactly the interdisciplinary topic you're working toward? If this is the case, just put cards into the slip box closest to their nearest related intellectual neighbor—and by this I mean nearest related to you, not to Melvil Dewey or anyone else. Over time, through growth and branching, ideas will fill in the interstitial spaces and neighboring ideas will slowly percolate and intermix. Your interests will slowly emerge into various bunches of cards in your box. Things you may have thought were important can separate away and end up on sparse branches while other areas flourish.

If you make the (false) choice to separate math and history into different "sections" it will be much harder for them to grow and intertwine in an organic and truly disciplinary way. Universities have done this sort of separation for hundreds of years and as a result, their engineering faculty can be buildings or even entire campuses away from their medical faculty who now want to work together in new interdisciplinary ways. This creates a physical barrier to more efficient and productive innovation and creativity. It's your zettelkasten, so put those ideas right next to each other from the start so they can do the work of serendipity and surprise for you. Do not artificially separate your favorite ideas. Let them mix and mingle and see what comes out of them.

If you feel the need to categorize and separate them in such a surgical fashion, then let your index be the place where this happens. This is what indices are for! Put the locations into the index to create the semantic separation. Math related material gets indexed under "M" and history under "H". Now those ideas can be mixed up in your box, but they're still findable. DO NOT USE OR CONSIDER YOUR NUMBERS AS TOPICAL HEADINGS!!! Don't make the fatal mistake of thinking this. The numbers are just that, numbers. They are there solely for you to be able to easily find the geographic location of individual cards quickly or perhaps recreate an order if you remove and mix a bunch for fun or (heaven forfend) accidentally tip your box out onto the floor. Each part has of the system has its job: the numbers allow you to find things where you expect them to be and the index does the work of tracking and separating topics if you need that.

The broader zettelkasten, tools for thought, and creativity community does a terrible job of explaining the "why" portion of what is going on here with respect to Luhmann's set up. Your zettelkasten is a crucible of ideas placed in juxtaposition with each other. Traversing through them and allowing them to collide in interesting and random ways is part of what will create a pre-programmed serendipity, surprise, and combinatorial creativity for your ideas. They help you to become more fruitful, inventive, and creative.

Broadly the same thing is happening with respect to the structure of commonplace books. There one needs to do more work of randomly reading through and revisiting portions to cause the work or serendipity and admixture, but the end results are roughly the same. With the zettelkasten, it's a bit easier for your favorite ideas to accumulate into one place (or neighborhood) for easier growth because you can move them around and juxtapose them as you add them rather than traversing from page 57 in one notebook to page 532 in another.

If you use your numbers as topical or category headings you'll artificially create dreadful neighborhoods for your ideas to live in. You want a diversity of ideas mixing together to create new ideas. To get a sense of this visually, play the game Parable of the Polygons in which one categorizes and separates (or doesn't) triangles and squares. The game created by Vi Hart and Nicky Case based on the research of Thomas Schelling provides a solid example of the sort of statistical mechanics going on with ideas in your zettelkasten when they're categorized rigidly. If you rigidly categorize ideas and separate them, you'll drastically minimize the chance of creating the sort of useful serendipity of intermixed and innovative ideas.

It's much harder to know what happens when you mix anthropology with complexity theory if they're in separate parts of your mental library, but if those are the things that get you going, then definitely put them right next to each other in your slip box. See what happens. If they're interesting and useful, they've got explicit numerical locators and are cross referenced in your index, so they're unlikely to get lost. Be experimental occasionally. Don't put that card on Henry David Thoreau in the section on writers, nature, or Concord, Massachusetts if those aren't interesting to you. Besides everyone has already done that. Instead put him next to your work on innovation and pencils because it's much easier to become a writer, philosopher, and intellectual when your family's successful pencil manufacturing business can pay for you to attend Harvard and your house is always full of writing instruments from a young age. Now you've got something interesting and creative. (And if you must, you can always link the card numerically to the other transcendentalists across the way.)

In case they didn't hear it in the back, I'll shout it again: ACTIVELY WORK AGAINST YOUR NATURAL URGE TO USE YOUR ZETTELKASTEN NUMBERS AS TOPICAL HEADINGS!!!

Thoughts on Zettelkasten numbering systems

I've seen variations of the beginner Zettelkasten question:

"What happens when you want to add a new note between notes 1/1 and 1/1a?"

asked at least a dozen times in the Reddit fora related to note taking and zettelkasten, on zettelkasten.de, or in other places across the web.

Dense Sets

From a mathematical perspective, these numbering or alpha-numeric systems are, by both intent and design, underpinned by the mathematical idea of dense sets. In the areas of topology and real analysis, one considers a set dense when one can choose a point as close as one likes to any other point. For both library cataloging systems and numbering schemes for ideas in Zettelkasten this means that you can always juxtapose one topic or idea in between any other two.

Part of the beauty of Melvil Dewey's original Dewey Decimal System is that regardless of how many new topics and subtopics one wants to add to their system, one can always fit another new topic between existing ones ad infinitum.

Going back to the motivating question above, the equivalent question mathematically is "what number is between 0.11 and 0.111?" (Here we've converted the artificial "number" "a" to a 1 and removed the punctuation, which doesn't create any issues and may help clarify the orderings a bit.) The answer is that there is an infinite number of numbers between these!

This is much more explicit by writing these numbers as:<br /> 0.110<br /> 0.111

Naturally 0.1101 is between them (along with an infinity of others), so one could start here as a means of inserting ideas this way if they liked. One either needs to count up sequentially (0, 1, 2, 3, ...) or add additional place values.

Decimal numbering systems in practice

The problem most people face is that they're not thinking of these numbers as decimals, but as natural numbers or integers (or broadly numbers without any decimal portions). Though of course in the realm of real numbers, numbers above 0 are dense as well, but require the use of their decimal portions to remain so.

The tough question is: what sorts of semantic meanings one might attach to their adding of additional place values or their alphabetical characters? This meaning can vary from person to person and system to system, so I won't delve into it here.

One may find it useful to logically chunk these numbers into groups of three as is often done using commas, periods, slashes, dashes, spaces, or other punctuation. This doesn't need to mean anything in particular, but may help to make one's numbers more easily readable as well as usable for filing new ideas. Sometimes these indicators can be confusing in discussion, so if ever in doubt, simply remove them and the general principles mentioned here should still hold.

Depending on one's note taking system, however, when putting cards into some semblance of a logical sort-able order (perhaps within a folder for example), the system may choke on additional characters beyond the standard period to designate a decimal number. For example: within Obsidian, if you have a "zettelkasten" folder with lots of numbered and named files within it, you'll want to give each number the maximum number of decimal places so that when doing an alphabetic sort within the folder, all of the numbered ideas are properly sorted. As an example if you give one file the name "0.510 Mathematics", another "0.514 Topology" and a third "0.5141 Dense Sets" they may not sort properly unless you give the first two decimal expansions to the ten-thousands place at a minimum. If you changed them to "0.5100 Mathematics" and "0.5140 Topology, then you're in good shape and the folder will alphabetically sort as you'd expect. Similarly some systems may or may not do well with including alphabetic characters mixed in with numbers.

If using chunked groups of three numbers, one might consider using the number 0.110.001 as the next level of idea between them and then continuing from there. This may help to spread some of the ideas out as surely one may have yet another idea to wedge in between 0.110.000 and 0.110.001?

One can naturally choose almost any any (decimal) number, so long as it it somewhat "near" the original behind which one places it. By going out further in the decimal expansion, one can always place any idea between two others and know that there will be a number that it can be given that will "work".

Generally within numbers as we use them for mathematics, 0.100000001 is technically "closer" by distance measurement to 0.1 than 0.11, (and by quite a bit!) but somehow when using numbers for zettelkasten purposes, we tend to want to not consider them as decimals, as the Dewey Decimal System does. We also have the tendency to want to keep our numbers as short as possible when writing, so it seems more "natural" to follow 0.11 with 0.111, as it seems like we're "counting up" rather than "counting down".

Another subtlety that one sees in numbering systems is the proper or improper use of the whole numbers in front of the decimal portions. For example, in Niklas Luhmann's system, he has a section of cards that start with 3.XXXX which are close to a section numbered 35.YYYY. This may seem a bit confusing, but he's doing a bit of mental gymnastics to artificially keep his numbers smaller. What he really means is 3000.XXX and 3500.YYY respectively, he's just truncating the extra zeros. Alternately in a fully "decimal system" one would write these as 0.3000.XXXX and 0.3500.YYYY, where we've added additional periods to the numbers to make them easier to read. Using our original example in an analog system, the user may have been using foreshortened indicators for their system and by writing 1/1a, they may have really meant something of the form 001.001/00a, but were making the number shorter in a logical manner (at least to them).

The close observer may have seen Scott Scheper adopt the slightly longer numbers in the thousands (like 3500.YYYY) as a means of remedying some of the numbering confusion many have when looking at Luhmann's system.

Those who build their systems on top of existing ones like the Dewey Decimal Classification, or the Universal Decimal Classification may wish to keep those broad categories with three to four decimal places at the start and then add their own idea number underneath those levels.

As an example, we can use the numbering for Finsler geometry from the Dewey Decimal Classification wikipedia page shown as:

``` 500 Natural sciences and mathematics

510 Mathematics

    516 Geometry

        516.3 Analytic geometries

            516.37 Metric differential geometries

                516.375 Finsler geometry

```

So in our zettelkasten, we might add our first card on the topic of Finsler geometry as "516.375.001 Definition of Finsler geometry" and continue from there with some interesting theorems and proofs on those topics.

Of course, while this is something one can do doesn't mean that one should do it. Going too far down the rabbit holes of "official" forms of classification this way can be a massive time wasting exercise as in most private systems, you're never going to be comparing your individual ideas with the private zettelkasten of others and in practice the sort of standardizing work for classification this way is utterly useless. Beyond this, most personal zettelkasten are unique and idiosyncratic to the user, so for example, my math section labeled 510 may have a lot more overlap with history, anthropology, and sociology hiding within it compared with others who may have all of their mathematics hiding amidst their social sciences section starting with the number 300. One of the benefits of Luhmann's numbering scheme, at least for him, is that it allowed his system to be much more interdisciplinary than using a more complicated Dewey Decimal oriented system which may have dictated moving some of his systems theory work out of his politics area where it may have made more sense to him in addition to being more productive on a personal level.

Of course if you're using the older sort of commonplacing zettelkasten system that was widely in use before Luhmann's variation, then perhaps using a Dewey-based system may be helpful to you?

A Touch of History

As both a mathematician working in the early days of real analysis and a librarian, some of these loose ideas may have occurred tangentially to Gottfried Wilhelm Leibniz (1646 - 1716), though I'm currently unaware of any specific instances within his work. One must note, however, that some of the earliest work within library card catalogs as we know and use them today stemmed from 1770s Austria where governmental conscription needs overlapped with card cataloging systems (Krajewski, 2011). It's here that the beginnings of these sorts of numbering systems begin to come into use well before Melvil Dewey's later work which became much more broadly adopted.

The German "file number" (aktenzeichen) is a unique identification of a file, commonly used in their court system and predecessors as well as file numbers in public administration since at least 1934. We know Niklas Luhmann studied law at the University of Freiburg from 1946 to 1949, when he obtained a law degree, before beginning a career in Lüneburg's public administration where he stayed in civil service until 1962. Given this fact, it's very likely that Luhmann had in-depth experience with these sorts of file numbers as location identifiers for files and documents. As a result it's reasonably likely that a simplified version of these were at least part of the inspiration for his own numbering system. † ‡

Your own practice

At the end of the day, the numbering system you choose needs to work for you within the system you're using (analog, digital, other). I would generally recommend against using someone else's numbering system unless it completely makes sense to you and you're able to quickly and simply add cards to your system with out the extra work and cognitive dissonance about what number you should give it. The more you simplify these small things, the easier and happier you'll be with your set up in the end.

References

Krajewski, Markus. Paper Machines: About Cards & Catalogs, 1548-1929. Translated by Peter Krapp. History and Foundations of Information Science. MIT Press, 2011. https://mitpress.mit.edu/books/paper-machines.

Munkres, James R. Topology. 2nd ed. 1975. Reprint, Prentice-Hall, Inc., 1999.

Hello u/sscheper,

Let me start by thanking you for introducing me to Zettelkasten. I have been writing notes for a week now and it's great that I'm able to retain more info and relate pieces of knowledge better through this method.

I recently came to notice that there is redundancy in my index entries.

I have two entries for Number Line. I have two branches in my Math category that deals with arithmetic, and so far I have "Addition" and "Subtraction". In those two branches I talk about visualizing ways of doing that, and both of those make use of and underline the term Number Line. So now the two entries in my index are "Number Line (Under Addition)" and "Number Line (Under Subtraction)". In those notes I elaborate how exactly each operation is done on a number line and the insights that can be derived from it. If this continues, I will have Number Line entries for "Multiplication" and "Division". I will also have to point to these entries if I want to link a main note for "Number Line".

Is this alright? Am I underlining appropriately? When do I not underline keyterms? I know that I do these to increase my chances of relating to those notes when I get to reach the concept of Number Lines as I go through the index but I feel like I'm overdoing it, and it's probably bloating it.

I get "Communication (under Info. Theory): '4212/1'" in the beginning because that is one aspect of Communication itself. But for something like the number line, it's very closely associated with arithmetic operations, and maybe I need to rethink how I populate my index.

Presuming, since you're here, that you're creating a more Luhmann-esque inspired zettelkasten as opposed to the commonplace book (and usually more heavily indexed) inspired version, here are some things to think about:<br /> - Aren't your various versions of number line card behind each other or at least very near each other within your system to begin with? (And if not, why not?) If they are, then you can get away with indexing only one and know that the others will automatically be nearby in the tree. <br /> - Rather than indexing each, why not cross-index the cards themselves (if they happen to be far away from each other) so that the link to Number Line (Subtraction) appears on Number Line (Addition) and vice-versa? As long as you can find one, you'll be able to find them all, if necessary.

If you look at Luhmann's online example index, you'll see that each index term only has one or two cross references, in part because future/new ideas close to the first one will naturally be installed close to the first instance. You won't find thousands of index entries in his system for things like "sociology" or "systems theory" because there would be so many that the index term would be useless. Instead, over time, he built huge blocks of cards on these topics and was thus able to focus more on the narrow/niche topics, which is usually where you're going to be doing most of your direct (and interesting) work.

Your case sounds, and I see it with many, is that your thinking process is going from the bottom up, but that you're attempting to wedge it into a top down process and create an artificial hierarchy based on it. Resist this urge. Approaching things after-the-fact, we might place information theory as a sub-category of mathematics with overlaps in physics, engineering, computer science, and even the humanities in areas like sociology, psychology, and anthropology, but where you put your work on it may depend on your approach. If you're a physicist, you'll center it within your physics work and then branch out from there. You'd then have some of the psychology related parts of information theory and communications branching off of your physics work, but who cares if it's there and not in a dramatically separate section with the top level labeled humanities? It's all interdisciplinary anyway, so don't worry and place things closest in your system to where you think they fit for you and your work. If you had five different people studying information theory who were respectively a physicist, a mathematician, a computer scientist, an engineer, and an anthropologist, they could ostensibly have all the same material on their cards, but the branching structures and locations of them all would be dramatically different and unique, if nothing else based on the time ordered way in which they came across all the distinct pieces. This is fine. You're building this for yourself, not for a mass public that will be using the Dewey Decimal System to track it all down—researchers and librarians can do that on behalf of your estate. (Of course, if you're a musician, it bears noting that you'd be totally fine building your information theory section within the area of "bands" as a subsection on "The Bandwagon". 😁)

If you overthink things and attempt to keep them too separate in their own prefigured categorical bins, you might, for example, have "chocolate" filed historically under the Olmec and might have "peanut butter" filed with Marcellus Gilmore Edson under chemistry or pharmacy. If you're a professional pastry chef this could be devastating as it will be much harder for the true "foodie" in your zettelkasten to creatively and more serendipitously link the two together to make peanut butter cups, something which may have otherwise fallen out much more quickly and easily if you'd taken a multi-disciplinary (bottom up) and certainly more natural approach to begin with. (Apologies for the length and potential overreach on your context here, but my two line response expanded because of other lines of thought I've been working on, and it was just easier for me to continue on writing while I had the "muse". Rather than edit it back down, I'll leave it as it may be of potential use to others coming with no context at all. In other words, consider most of this response a selfish one for me and my own slip box than as responsive to the OP.)

In a break from the more traditional subject heading filing system of many commonplacing and zettelkasten methods, in addition to this sort of scheme Heyde also suggests potentially using the Dewey Decimal System for organizing one's knowledge.

While Luhmann doesn't use Dewey's system, he does follow the broader advice which allows creating a dense numbering system though he does use a different numbering scheme.

that the sheetification can also be done based on other principles.

Heyde specifically calls the reader to consider other methods in general and points out the Dewey Decimal Classification system as a possibility. This suggestion also may have prompted Luhmann to do some evolutionary work for his own needs.

While Heyde outlines using keywords/subject headings and dates on the bottom of cards with multiple copies using carbon paper, we're left with the question of where Luhmann pulled his particular non-topical ordering as well as his numbering scheme.

While it's highly likely that Luhmann would have been familiar with the German practice of Aktenzeichen ("file numbers") and may have gotten some interesting ideas about organization from the closing sections of the "Die Kartei" section 1.2 of the book, which discusses library organization and the Dewey Decimal system, we're still left with the bigger question of organization.

It's obvious that Luhmann didn't follow the heavy use of subject headings nor the advice about multiple copies of cards in various portions of an alphabetical index.

While the Dewey Decimal System set up described is indicative of some of the numbering practices, it doesn't get us the entirety of his numbering system and practice.

One need only take a look at the Inhalt (table of contents) of Heyde's book! The outline portion of the contents displays a very traditional branching tree structure of ideas. Further, the outline is very specifically and similarly numbered to that of Luhmann's zettelkasten. This structure and numbering system is highly suggestive of branching ideas where each branch builds on the ideas immediately above it or on the ideas at the next section above that level.

Just as one can add an infinite number of books into the Dewey Decimal system in a way that similar ideas are relatively close together to provide serendipity for both search and idea development, one can continue adding ideas to this branching structure so they're near their colleagues.

Thus it's highly possible that the confluence of descriptions with the book and the outline of the table of contents itself suggested a better method of note keeping to Luhmann. Doing this solves the issue of needing to create multiple copies of note cards as well as trying to find cards in various places throughout the overall collection, not to mention slimming down the collection immensely. Searching for and finding a place to put new cards ensures not only that one places one's ideas into a growing logical structure, but it also ensures that one doesn't duplicate information that may already exist within one's over-arching outline. From an indexing perspective, it also solves the problem of cross referencing information along the axes of the source author, source title, and a large variety of potential subject headings.

And of course if we add even a soupcon of domain expertise in systems theory to the mix...

While thinking about Aktenzeichen, keep in mind that it was used in German public administration since at least 1934, only a few years following Heyde's first edition, but would have been more heavily used by the late 1940's when Luhmann would have begun his law studies.

https://hypothes.is/a/CqGhGvchEey6heekrEJ9WA

When thinking about taking notes for creating output, one can follow one thought with another logically both within one's card index not only to write an actual paper, but the collection and development happens the same way one is filling in an invisible outline which builds itself over time.

Linking different ideas to other ideas separate from one chain of thought also provides the ability to create multiple of these invisible, but organically growing outlines.

Portions of Dewey's system as described here can definitely be seen in Luhmann's system in which he left some of the preceding numbers unwritten/unstated.

The Outline of Knowledge appears in the Propædia volume of the Encyclopedia Britannica. It is similar to various olther classification systems like the Dewey Decimal system or the Universal Decimal Classification.

https://niklas-luhmann-archiv.de/bestand/zettelkasten/zettel/ZK_2_SW1_001_V

One may notice that Niklas Luhmann's index within his zettelkasten is fantastically sparce. By this we might look at the index entry for "system" which links to only one card. For someone who spent a large portion of his life researching systems theory, this may seem fantastically bizarre.

However, it's not as as odd as one may think given the structure of his particular zettelkasten. The single reference gives an initial foothold into his slip box where shuffling through cards beyond that idea will reveal a number of cards closely related to the topic which subsequently follow it. Regular use and work with the system would have allowed Luhmann better memory with respect to its contents and the searching through threads of thought would have potentially sparked new ideas and threads. Thus he didn't need to spend the time and effort to highly index each individual card, he just needed a starting place and could follow the links from there. This tends to minimize the indexing work he needed to do regularly, but simultaneously makes it harder for the modern person who may wish to read or consult those notes.

Some of the difference here is the idea of top-down versus bottom-up construction. While thousands of his cards may have been tagged as "systems" or "systems theory", over time and with increased scale they would have become nearly useless as a construct. Instead, one may consider increasing levels of sub-topics, but these too may be generally useless with respect to (manual) search, so the better option is to only look at the smallest level of link (and/or their titles) which is only likely to link to 3-4 other locations outside of the card just before it. This greater specificity scales better over time on the part of the individual user who is broadly familiar with the system.

Alternatively, for those in shared digital spaces who may maintain public facing (potentially shared) notes (zettelkasten), such sparse indices may not be as functional for the readers of such notes. New readers entering such material generally without context, will feel lost or befuddled that they may need to read hundreds of cards to find and explore the sorts of ideas they're actively looking for. In these cases, more extensive indices, digital search, and improved user interfaces may be required to help new readers find their way into the corpus of another's notes.

Another related idea to that of digital, public, shared notes, is shared taxonomies. What sorts of word or words would one want to search for broadly to find the appropriate places? Certainly widely used systems like the Dewey Decimal System or the Universal Decimal Classification may be helpful for broadly crosslinking across systems, but this will take an additional level of work on the individual publishers.

Is or isn't it worthwhile to do this in practice? Is this make-work? Perhaps not in analog spaces, but what about the affordances in digital spaces which are generally more easily searched as a corpus.

As an experiment, attempt to explore Luhmann's Zettelkasten via an entryway into the index. Compare and contrast this with Andy Matuschak's notes which have some clever cross linking UI at the bottoms of the notes, but which are missing simple search functionality and have no tagging/indexing at all. Similarly look at W. Ross Ashby's system (both analog and digitized) and explore the different affordances of these two which are separately designed structures---the analog by Ashby himself, but the digital one by an institution after his death.

https://udcsummary.info/php/index.php?lang=en

Interesting defined vocabulary and concatenation/auxiliary signs for putting ideas into proximity.

Could be useful for note taking. Probably much harder to get people to adopt this sort of thing with shared notes/note taking however.

Somewhat similar to the Dewey Decimal classification system.

This seems illustrative of the idea that some of the most interesting things in life or living systems exist at the chaotic borders.

There seem to be differences between more rigid structures like the Dewey Decimal Classification system or Paul Otlet's Mundaneum and less rigid branching systems like Luhmann's version of his zettelkasten. Is this really a difference or only a seeming difference given the standardization some of the systems. There should be a way to do both. Maybe it's by the emergence of public standards, or perhaps it's simply through the use of subject headings and the cross linking of emerging folksonomies.

What does the use of platforms like the Federated Wiki or the early blogosphere and linking and discovery methods enabled by Technorati indicate?

Luhmann's system may seem intrapersonal, perhaps as a result of the numbering system, but it becomes highly penetrable by the subject index and the links from one idea (card) to the next. Use over time makes it even easier.

Ryan Holiday notes the similarity of his method to that of the Dewey Decimal system and library card catalogs.