In Japan they say that there are two things you should never discuss with someone from the States: whales and religion. Both are likely to get you in trouble with someone passionate.

I am tempted to add a third item: threaded versus linear discussions. Some people are passionate about their preferences for threading versus chronological discussions, with a high level of conviction. Often I find myself in conversations about this with customers, and an exploration of the two discussion styles seems in order.

Many early web-based forum applications used the threaded model, probably because that's what participants understood from experience with Usenet. The roots of Usenet go back to 1979 when two Duke University grad students created an Internet community system that permits users to post messages (news) within categories called newsgroups. A Usenet thread is a series of messages, where you always reply to specific messages. With many levels of messages and replies and replies-to-replies, you get an outline structure with messages and their replies nesting many levels deep. When web-based forums began appearing in the 1990's, it was natural that many of them would be modeled on the Usenet approach.

Despite the power of the threaded model, some community architects took a different approach, and even before the advent of the Internet some bulletin board systems used a linear interface. Also called the conversational style, this approach offers a user interface in which all messages appear in chronological order. Instead of nesting new topic areas within a thread, users are expected to stay on topic; instead of "hijacking" a thread to change the discussion you're expected to create a new thread. This linear approach more closely approximates real life - until time travel is perfected actual conversations are necessarily in chronological order - and quite likely because the functionality is obvious to everyone the linear style has become very popular.

Both styles have their advantages. How does a new community manager decide on the best approach? I've found it's best to consider both the demographic of the community and common modes of community access to come to a decision. My experience is that in the more technically oriented community, the average participant will appreciate and exploit the power of the threaded interface rather than being confused by it. In a community of largely non-technical users, you will get more participation with a conversational model.

Beyond the skillsets of users, the various mechanisms that may be used to access the community may be significant in the choice of interface. Modern community applications typically permit full participation by both email and browser clients, and sometimes news (NNTP) is supported as well. If only one of these modes is enabled the choice of interface can probably be resolved just by considering the demographic, but in other cases the decision may be more challenging. Typically it's the email participation that can throw in a monkey wrench. With the threaded style a nested and indented reply to an old message - perfectly clear when viewed with a browser - shows up in email with no context at all and confusion may ensue.

From my perspective, the trend among new communities is towards selecting the linear style. Users who are new to forums are quite likely to have experience with blog comments that almost universally linear, and virtually anyone can grasp the basics of linear forum participation quickly. The threaded style isn't going away though, and the choice between the two modes remains an important part of the decision-making process in any new community deployment.