My blog allows me to put postings into categories. After a few years of doing this, and after
participating in the license proliferation committee, I'm convinced that ``categories'' is a
wrong solution for organizing blog postings and licenses. I'm also convinced that
``subdirectories'' is a wrong solution for organizing files. A category is a single
attribute.
What you really want is tags. Yes, everything needs a unique tag which nothing else has, but
we have a perfectly fine system for uniqueness: time. Every moment is unique. So, a license
like the GPL might have "reciprocal,popular,stewarded,fsf" on it. Etc.