Tagging is easier than categorization because you don’t have to make as many decisions.
A cognitive analysis of tagging (http://www.rashmisinha.com/)
(or how the lower cognitive cost of tagging makes it popular)
With tagging … you can note as many of those associations as you want. This is how tagging works, cognitively speaking. Yes, it’s that simple.
What I suspect the author is saying is that we don’t like to make decisions. I don’t. I get home from work and sometimes I can’t figure out what t-shirt to change into. As I post this on typepad there is a keywords box shown below that does cause me a bit of stress at the end of a post. Basically keywords are tags, or relevant topics at a minimum. I suppose keywords have a sort-of-unwritten rule that they are supposed to be nouns while tags can be nouns, verbs, adjectives, etc.
Other challenges of tags, or really any ontology:
1) You can’t guarantee other humans will categorize like you do, so even if you can remember your own categories your methods may be in no way helpful to others. For your mp3 collection this is fine, but for social software you are breaking the social contract and not providing value to others. We will find a way to derive value, but you get my point.
2) Time changes how you categorize stuff. As a young man you might put owning a yacht into the "success" category while a former boat owner would categorize this as "classified listing".
2) A sense of fairness can screw up categories. This is just a brain game we all play. If I categorize 50 items and they get divided as 25, 10, 10, 4 and 1 – I will really look at the category with one (1) item to see if I can’t refile it in one of the larger categories. It is the odd-man-out so surely it must fit in another category or nobody will ever find it in the future, right? I can’t explain this reflex.
4) Cultural relevance, although I believe tagging and categories both suffer from this limitation. Rashmi, the author of the above article, discusses cultural relevance in her article but this probably warrants a complete novel unto itself. We need a cultural-tag-encyclopedia in the future. "Cadiallac means AAAAAAA in Detroit and Cadillac means BBBBBBB in Tokyo… or similar.
I will defer to Rashmi’s analysis on the cognitive aspects of tagging. Definitely worth further thought.