Ars Technica has a four-part introductory series on logic and argumentation, entitled “Getting to QED.”

In some cases, there is a way to tell good arguments from bad using what is called informal logic. This name distinguishes it from formal logic, which is used in mathematics; natural language is less precise than mathematics, and does not always follow the same rules. Perhaps more surprisingly, the name also reflects the fact that there is a lot of disagreement over what it means. Informal logic is actually a fairly young discipline, developed in the 1960s, and intended to apply new techniques from formal logic to argument and critical thinking. Philosophers are still wrestling with this application, and there are several competing schools of thought.

For all the differences, there are some core elements upon which everyone agrees. This article is a tutorial introducing these basic ideas of informal logic. In particular, we focus on deductive reasoning, which is one of the cornerstones of analytical thought. Hopefully you will come away from this article with the tools to distinguish a productive debate from an acrimonious flame war.

This should be required reading for anyone who’s engaged in debate on a mailing list or web forum.