Tagging is a strictly more powerful tool than hierarchies, at least with same amount tags vs directories/categories, because an item can be tagged using multiple different tags, but can only be in one directory, unless you create duplicates or symlinks or whatever.

I find the opposite. Being forced to consider hierarchical categorisation leads to a more powerful system in practice. It helps me create a mental reference to the item being stored. And it often causes me to see a better way to form an item in the first place — eg maybe this note is really two notes, maybe this idea can actually just be discarded, etc. Or, on rare occasions, a new item doesn’t fit anywhere (but is important) so I need to tweak the hierarchy itself — and that’s a good thing, once in a while, as it can lead to creative insights about the domain as a whole.

I’ve found tagging systems usually become a kind of dark swamp where things go never to be seen again. The lack of structure means I have little memory of what’s gone into the system, so I end up with too much duplication of ideas and inconsistency of style (mess). All this makes it uninviting and difficult to ‘explore’, so I don’t use it much except as a dumping ground, and the swampiness compounds over time.

Hierarchy doesn’t make sense if you care about multiple dimensions, which I often do with notes.

Sometimes I want to look at all notes relating to c++, sometimes everything related to a personal project. Directories don’t support that without symlinking everything that mentions c++ into a folder for that.

Hierarchy can do that too, once you allow a single file to exist in multiple hierarchies at once. Think of database, we have a single table, yet we have a lot of different indexes to search on.

We could do the same, either with symlinks or hardlinks

I really like tagging but somehow the concept could never become central to any filesystem:

- I believe BeOS tried,

- MS tried with WinFS but cancelled it in Windows Vista,

- I am sure some cloud storage service bet on it but can't cite any.

Actually tagging is probably mainly successful in cases where we can reliably automate the tagging such as email or photos.

MacOS has had first-class support for file tagging for years: You can add arbitrary tags either from “Save as” dialogs or from Finder, and can then browse by tags in Finder or search through your file system filtered by tags.

Does the native file tagging see much adoption? I'm a lifelong Mac user and tried using the tags when they first launched, but eventually it was too much work and I resorted to using search to find what I'm looking for. Not macOS native search but tools like LaunchBar, Alfred, et al or apps like EasyFind.

Colours, yes – but then again I worked in a print shop that'd been using Apple since MacOS 8, so they might be used to those quirks.

I like tagging for bookmarks in Firefox and derivatives of Firefox.

Sharepoint tries to push people towards tags, but doesn't always succeed.

Everything is a hierarchy, even the tags in your mind do belong under some tree/node like imagination. Tag is essentially just what you described "duplicates or symlinks or whatever."

This isn't really true. Even mature, sophisticated attempts at making hierarchical classification systems (e.g. the UDC[0]) don't claim to have created a system where each document gets a unique leaf on a tree, and indeed instead attempt provide some syntax for adding additional metadata into its "nodes," i.e. the nodes become the sum of their tags.

[0] https://en.wikipedia.org/wiki/Universal_Decimal_Classificati...

> but can only be in one directory, unless you create duplicates or symlinks or whatever.

Non-sym links do exactly this. Starting with your file in foo;

    ln foo/file bar/file

will have the file (really a reference-counted pointer) appear in both directories. It's the same location on disk and there's no overhead until you run out of inodes.