Faced with the rapidity at which anonymous conversations on the internet deteriorate, Paul Graham’s broken things down into six levels of argument. It starts with name-calling at the bottom and ends with the Refutation of the Central Point at the top.
This is a wonderful model. I especially like the diagram because it’s really easy to pick out which level your argument is on. I’m going to make a poster sized version of this and post it on the wall. And, there’ll be a lesson.