The term “Motte and Bailey” has become rather popular in recent years to describe a certain style of argument wherein an arguer strategically equivocates between a boring but easily defensible claim and a more radical but indefensible claim. “Motte and Bailey” is a reference to a type of medieval defensive warfare, where an impregnable fortress (the motte) overlooks some desirable but lightly defensible territory (the bailey). The bailey can be defended against light skirmishes. But against a sustained attack, defenders would fall back to the motte and hold out there, raining arrows on the attackers until the attackers give up and retreat, at which point the bailey could be occupied again. Similarly, in argument, one might retreat to a narrow set of defensible commitments if challenged, but then resume saying indefensible things once the skeptic is out of earshot.
This concept was popularized by the SlateStarCodex blog. If you’ve heard the term, it’s probably because of the work done on that blog. But many don’t realize that the term was coined by a philosopher, Nicholas Shackel of Cardiff University, in a paper published in 2005, “The Vacuity of Postmodernist Methodology.” Shackel’s paper has been cited only 41 times since then – not bad, to be sure, but one suspects that the number would be higher if more philosophers were aware of it. It’s great.