Ever since I have been using WordPress it has been based on categories. Tags are a relatively new thing, that I have never used, and even newer in the core. Interestingly Habari currently has only tags and I think this difference is quite an interesting one.
Generally people tend to think of categories fairly strict divisions that define the main topic of a post and tags as more specific, but loosly used, labels that are actually closer to index entries than an organisational structure.
The nature of blogs means that it is rarely possible to pre-define the content that will be included and this means that categories often get a little overgrown and need pruning back once in a while. Tags on the other hand are much more fluid and so can be left to grow where they will.
When it all comes down to it though they are both labels that apply to content. The only difference is in the way that we think about them, and use them. In fact the biggest difference is the user interface.
I’ve spent that last month doing little else but organising information and trying very hard not to assign lables to the various parts of the hierarchies so as not to confuse people with terms they expect to refer to something else and even so it has taken me some thought to get my head around the difference, or lack of difference, between tags and categories.
Only using tags (or only using categories) seems to offer a lot of flexibility. It lets you use plugins and naming structures to create hierarchies without the need for WordPress or Habari to actually be written to meet individial needs.
The differences, and uses, of tags and categories are well ingrained in people’s minds now and, let’s be honest, a lot of people do not want to consider their site taxonomy in greater depth than the default provides, but I think it would be interesting to just stop using categories in WordPress and switch to tags. It would certainly simplify some things.