Steve Bennett wrote:
The problem there, now that I think about it, is that Paris should not be in the category "Paris" (as was pointed out by someone else).
Actually, if we consider "Paris" a thematic category, then it makes sense for Paris to be in it, since it certainly fits the theme.
But I do agree that the category "Paris" should not be a subcategory of "European capitals", since the things in the "Paris" category (with one possible exception) are not European capitals.
Hmm, the difficulty is deciding what "subcategory" really means. I assume you're getting at the fact that a taxonomic subcategory should simply be getting more specific, and leading to more specialised subjects (so "Capitals of Europe" might have subcat "Capitals of Western Europe" or "Capitals of the European Union"), maintaining the "X is a Capital of Europe" mantra.
In this case, it would seem best that "Districts of Paris" was a category of the thematic category "Paris".
...which could, however, be a subcategory of "France", which in turn could be a subcategory of "Europe" -- all of these being thematic categories, and each theme being a subset of its parent theme.
In fact, we _could_ have a parallel taxonomic category tree that focused solely on geography, with "Districts of Paris" being a subset of "Places in Paris", which in turn is a subset of "Places in France" (but _not_ "Cities in France") and "Places in Europe" and ultimately "Places". So we'd have a tree of taxonomic "Places in [Region]" categories, each one having subcategories named either "[Divisions] in [Region]" or "Places in [Subregion]", with the root of the tree being "Places". (I'm torn on whether we'd need a second-level category "Places on Earth", though.)
So, to summarize what I believe has been proposed:
Taxonomic categories (plural): * Subcategories are subsets (and always taxonomic). * Members are instances.
Thematic categories (singular): * Subcategories are subthemes (thematic) or sets of related things (taxonomic). * Members are related things.
The plural/singular distinction may not be ideal, but does feel very natural in many cases. It's not without problems, though: what about, for example, the category "Sheep"?