I wouldn’t have expected a thing like a hashtag in Twitter or FriendFeed to become a rhetorical device as well as a functional one, but that’s exactly what I see happening. (For those of you that just asked “Hashtag? What now?” here’s a nice summary of how it works on Twitter.)

Looking back, I can see now that hashtags not only allowed people to gather together categories of posts, but they also gave a kind of short-hand context to those posts. A brief post like “Mediocre at best” reads differently if it’s tagged “#IL2009” or “#ProjectRunway.” The first sounds like a conference attendee who’s underwhelmed by a session. The second sounds like a critique of a fashion design on a reality TV show. Totally different contexts lead to totally different readings.

And as it turns out, short-hand contexts are pretty useful rhetorical things online, particularly in asynchronous conversations or when you’re only allowed a few words at a time. Lately the amateur anthropologist in me has been fascinated by the ways I’ve seen hashtags used not so much to allow people to gather posts together but instead to imply a category or topic that in turn supply a context for the preceding post. They let posters signal “I’m joking” or “here’s how I want you to interpret my post” without ruining the moment with a dry pronouncements of intent.

For example, I’d have had no idea what a friend was talking about if he’d just said, “Remember that part in Star Wars where the characters are running from the troopers in Mos Eisley, and they scramble on board the Millennium Falcon and then have to wait several hours for the weather to improve before they can blast off? Yeah, me neither” (from stevelawson on friendfeed). But then he added “#nasaisharshingmyfuture,” to let us know that he’s talking about the way that modern day space travel isn’t living up to the promise of science fiction. Context. There are no other posts with that hashtag, so it’s certainly not serving a gathering function, but it implies a category, implies that there could be many more examples of this particular phenomenon, and therefore builds a whole imaginary context for the original statement.

Fascinating.

Like any rhetorical device, though, it’s a skill that needs developing. Some of the people I follow seem to be really good at it. I, on the other hand, could really use some practice.