Categories vs. Tags in WordPress

Two interesting questions came up in my Tagging 101 session at Northern Voice yesterday:

1. "What's the difference between categories and tags in WordPress?"
2. "They seem the same. Should I use them differently?"

I didn't have great answers but a couple of audience members had some good ideas, so I thought I'd write them up.

• Categories are persistent. You can add as many as you want but they always appear in the right menu when you create a post. WordPress also generates an RSS feed for each category, which lets people follow a subset of your posts. So categories are probably best used as stable buckets for the kinds of content you publish (photos, videos, etc.), or the major topics you write about ("web design", "knitting", and so on).
• When you tag in WordPress, you're adding a list of comma-delimited keywords to a post. These tags can appear in a tag cloud on your post (depending on your theme). But they're not persistent in the same way that categories are--that is, you don't see your old tags when you're adding new tags. Perhaps more importantly, there is no way to edit or delete tags you've entered, except for manually removing them from each post.
  
  Personally, I would use tags to add specific keywords that elaborate on the subject of the post--like the names of people, product or companies mentioned in the post, or descriptive topic names that aren't categories (e.g. "landscapes", "portraits" might be good tags for your "photography" category).

If you're just curious about tagging you blog posts, hopefully that addresses your needs. One quick note for WordPress.com users: WP.com aggregates tags and categories into pages, so your post on "tech" will be pulled together with other posts tagged or categorized "tech" by other WordPress users. Yes, this is kind of confusing, but that's just how it works.

Finally, WordPress has a good FAQ on the technical differences between categories and tags.