In my idle moments (haha) I visit a number of different science blogs - both the posts and the comments threads can be educational and entertaining as well. Sometimes, for particular topics (vaccination being one, but anything to do with 'natural health products' can almost be guaranteed to set things off as well), the discussion can be derailed by one or two commenters who seem unwilling or unable to follow the normal rules of a rational debate. This can make it really hard to keep a discussion on track & must be frustrating for others trying to follow the thread of ideas.
Anyway, while browsing Peter Bowditch's Millenium Project I came across a poster encapsulating those rules. I thought I'd share it here, not least because these rules can apply to debate in a classroom just as much as they can to a face-to-face, one-on-one discussion and an internet forum or comments thread. (Click on the graphic for a higher-quality image.) I can see myself applying some of these statements in some of the threads I visit :)