In our new age of two-way news, news organizations sometimes struggle to find a way to foster productive conversation: to move beyond superficial gestures of inclusiveness — empty questions, atomized responses — to create conversation that is meaningful and purposeful. This weekend, The Washington Post found a way to create that kind of conversation, by way of commemorating Saturday’s nine-year anniversary of September 11: It created a Twitter hashtag, #wherewereyou, asking readers to share where they were when they first learned that the towers had been hit.

Anthony Dale: I was late to work at the Pentagon. I heard the news when I was 10 minutes away.

Katie Roberts: 7th grade gym class.. and they wouldn’t let us turn on the news.

Stuart Berlow: 13th&K, watching the Pentagon smoke behind the Monument

Ethan Horowitz: was in college at the u of md. came out of class & everyone was standing around listening 2 news on a car radio turned way up.

The Post’s solution was elegant and organic at the same time: It took a basic question — a question everyone, anyone can answer — and molded it into a simple but powerful piece of journalism. The tag — a more creative, dynamic version of MSNBC’s yearly replay of its initial, frenzied 9/11 coverage — invited its participants to take part in the yearly ritual of collective memory. And it defined the news organization not merely as a collector of news, but as a curator of experience.

“I think the fact that we have a brand like The Washington Post pushing the conversation helped a lot,” notes Melissa Bell, the Postie who oversaw the effort, “but I think that the Twitter hashtag was something people responded to because everyone felt really passionately about it.”

The idea for the #wherewereyou curation actually started not with the anniversary of 9/11, Bell told me, but rather with the commemoration of another national tragedy: the five-year anniversary of Katrina. On the paper’s Voices section, Bell posted a pastiche of the Post’s front pages during Katrina. (“I love doing that,” she notes, “because it really brings you back to the moment — there’s an immediacy that the front pages give you that I don’t think any other story can tell you.”) In the same post, Bell put out a call for “where were you” stories: “Where were you when the storm hit? When did you realize the real magnitude of the event?” Rather than Twitter, though, the call used a Post community group forum — which solicited some lengthy, thoughtful responses…but not very many of them. Since, Bell notes, “we’re trying to push these things out in the world to get a bigger conversation going,” they wanted to think bigger. When the 9/11 anniversary came along, Bell and the rest of the Post’s engagement and interactivity teams were looking for a call-and-response platform that would feature, in the end, much more “response” than “call.”

The solution: Twitter. And, for that, “we were thinking about a question that would capture that sense of immediacy,” Bell notes. “People remember the John F. Kennedy assassination” — pretty much every American alive at the time has an answer to the “where were you when” question — and “I think, for our generation, ‘where were you on 9/11?’ is something that has a memory attached to it.” So they kept the “where were you” query about Katrina — a more evocative question when applied to 9/11, an event that hit at a single moment, rather than over several days — but sent it out both on the forum…and on the @washingtonpost Twitter feed.

They got an outpouring of immediate answers. “It was really amazing to see how quickly people responded to it,” Bell notes. Since the team wanted to collect the replies, though — the idea was to curate the most evocative replies on the new Blog Post blog (“The Washington Post’s sounding board for news and conversation that’s reverberating in your world — online, on TV, and in your community”) — they realized they needed a way to round them up. Thus, the #wherewereyou tag.

Within a few hours, the tag was a trending topic in DC. “People have to be engaged,” Bell notes. “They’re not going to respond to a hashtag like #washingtonpost911 or something like that; they have to respond to the simplicity of the hashtag.” The tag needed to be evocative in order to be inviting. And “it seemed like a lot of people would be able to identify what it meant,” Bell notes, “because of the conversation about 9/11 already happening on the web.”

The thing with hashtags, though — their genius and their drawback — is their semantic malleability. Hashtags mean what their users decide they mean; they’re entirely dependent on context. They are context. And a funny thing happened with this one: After the initial burst of 9/11-related answers…the tag lost some of its initial meaning. Tweets like “Where were you when you first heard Glenn Beck exploit 9/11?” and, more commonly, “I was always there when you needed me, #wherewereyou when I was in need of you?” began to pop up in the #wherewereyou stream. Follow the stream now, and you’d have very little idea of its original purpose. If the @washingtonpost Twitter feed was the locus, the current tweets are the spokes — and the further the tag spread from the center, the more the meaning became disconnected from its origin. Users took it and made it their own. (As did other news organizations: On Saturday morning, NBC News asked its followers, “Where were you nine years ago today? #wherewereyou“)

And yet: “The side conversation going on — these sort of plaintive love posts coming out of it — fit, in a weird way, with the conversation that was happening,” Bell notes. “They were totally apart from 9/11, but they were touching in their own heartbreaking way.” The news organization put out a call for responses, curated from that…and then let the initial call resolve on its own, organically. Check the #wherewereyou tag now, and the stream feels more like an indignant love song than an elegy to a national tragedy.

And that’s okay. The point is the invitation, the incitement to expression. The point is a media organization subtly expanding its mandate to include guiding conversations rather than simply providing the raw material for them. “We wanted to really let people know that we were listening, and that we were really enjoying the stories, and they were really touching us,” Bell says. “It wasn’t just being put out into the ether, with nobody paying attention”; on the contrary, “we wanted to let people know that we want to be a repository of conversation — on our site and off our site. We don’t want to exist in a vacuum.”