TAG! You're it!

Let's face it, this is an example of how language has changed over the years. When I was a kid, a tag was something that was sprayed on a wall or under a bridge. It was the signature of the artist who created the graffiti, and could itself be art. Now, it means something else. Something sinister.

In this instance, tag refers to the labels we put on things so we can find them later. You save things in del.icio.us and give them useful tags, like "work" or "18th Century monarchs", so that when you try to find that site about Louis XVI, you know where to look. Hmm. "France", "revolution", or "beheadings" might be good tags for that site, too. And that's exactly the point. Unlike traditional sorting methods, tags work from the bottom up.

Take the example of the humble domesticated dog, Canis lupus familiaris. If you examine the dog's scientific classification, it begins at the broadest possible point, that of being a multicellular organism, and works down through the animal kingdom, having a spinal column, being a mammal, then a carnivore, then the family of animals that resemble dogs, to the rather more specific wolves and jackals, to just plain old wolves, ending with the subspecies of domesticated wolves (dogs). Wow. It's tag would, of course, be "dog". Maybe also "puppy", "cute", "beagle", "pet", or any number of other common identifiers that say "this thing here, it's a dog". Tags start from the presupposition that what we have is a dog. Not a multicellular animal with a backbone. And that's three steps into it!

To put it another way, if I told you that I saw a Haliaeetus leucocephalus, would you know what I was talking about? How about if I gave you some more information?

Kingdom: Animalia

Doesn't help much?

Phylum: Chordata

Don't speak Latin?

Class: Aves

I'll give this one to you: it's a bird.

Order: Falconiformes

Modern Latin sure is funny.

Family: Accipitridae

And you already have the genus and species for H. leucocephalus. Leucocephalus is Greek for "white head". Give up?

It would have been much easier if I had just told you it was a bald eagle, right? I'm willing to wager that few people tag bald eagles with "has a spine". Probably stuff like "endangered" or "national bird" or something. No disrespect meant to other nations and their fine birds, of course.

Take lots of people tagging things, and you create a folksonomy, a sort of common sense system of classification where the most commonly used terms are the most dominant. I hate that word, folksonomy. It sounds like something the Germans did at the end of World War II, when all the regular taxonomists had gone to the front and it was left up to young boys and old men to come up with names for things. But that would be Volksnamen, wouldn't it?

This is a nightmare for serious researchers, but a godsend for the average Joe. Joe probably wouldn't know how to find a picture of Canis lupus familiaris, but can show you lots of pictures of his dog.

No one says get rid of the old methods of classification. That would be silly. Top-down classification is essential to really divide things into categories for study and identicifation. But for plebians, things like "dog" and "eagle" are enough. Common sense tells us that Algebra is a type of mathematics. Do we need to classify it as "Mathematics - Algebra"? Probably not, unless you need different kinds of maths grouped together.

Not that there's anything wrong with that.