A singular question
Since I published my advice on tagging best practices, the most common question I’ve received has been something along the lines of “why the heck would you use singular tags?” Everyone agrees that consistency is the name of the game, and it’s hard to argue with succinctness. Some people disagree with using lowercase tags, but quite honestly it’s mainly personal preference (unless the program uses case-sensitive searching).
Whether or not to use singular tags, though, is a much more open question, and I’d like to lay out the reasons that I included a recommendation to stick to singular.
First I should mention that I don’t think every tag should be singular; whether or not you use singular tags is highly situational. For instance, if you have a photograph with a group of people in it, then tagging it “person” is utterly ridiculous. When I advise using singular tags, my hope is that people will try to stick to singular tags only when appropriate. If singular tags are the baseline, then searching for “people” as opposed to “person” means you get two different sets of items rather than one set of items that includes both. (Of course it can work the other way if you use plural tags as your baseline, too. Whatever makes the most sense to you is what matters.)
Second, a major assumption that I held going into the best practices article was that you are tagging items in a desktop program for personal usage. In this case, there is no question over what you will search for because you have complete control over all three parts of tagging. However, if you are tagging items so that other people will find them (the case in most online tagging), you will need to think about tags differently. Sticking to plural tags may actually benefit you more for online tagging, because people tend to think of tags online as categories. Neglecting to mention that my SLS guidelines are most appropriate for personal use was an oversight of mine; there are large differences between personal, public, and collaborative tagging.
Ideally, of course, your tagging software would permit creating synonyms for tags. Unfortunately, we don’t live in an ideal world, and this is pretty rare (might even be non-existent; off the top of my head I can’t think of any software that supports tag synonyms).
At base, whether you tag by default with singular or plural really relies on how you think about tags: are you tagging what an item is or what an item is one of? In the first case, you should use singular as much as you can. In the second, you should stick to plural. For example, I could tag this article “clarification” because I am clarifying an earlier argument. Or I could decide that my “clarification” tag is more like a category; it contains multiple items, each of which is a clarification. In that case, I would tag this post “clarifications”.
I personally prefer to use singular tags as my default because I think of tags as terms that describe a specific item. For me, a tag says, “This item is a [blank]“. I am not sorting items into categories; rather I am attaching descriptive terms to items. The wonderful thing about tags, though, is that if thinking about tags like this makes no sense to you, you don’t have to follow my advise.
I knew when I included both lowercase and singular into my little “SLS” scheme that they were mostly reliant on individual preference. The reason that I included them, however, is because both the capitalization and plurality of your tags are things you must consider when you are building a tagging system. I don’t care whether you tag things the way I do; what I care about is that you think about the issue before you start tagging inconsistently and causing a lot of pain for yourself.
I hope this has helped to clarify my standpoint on the plurality of tags! If you have any thoughts on the matter, I would love to hear from you!