I just want to park this one here, so I don’t forget about it. I see it a lot. Someone makes a specious argument, and when challenged falls back on something that is obviously true and defensible. But once they’ve exhausted me, they come back and conflate their bad reasoning with the agreed-upon truth.
The term comes from this analogy:
[A motte-and-bailey is] a form of medieval castle, where there would be a field of desirable and economically productive land called a bailey, and a big ugly tower in the middle called the motte. If you were a medieval lord, you would do most of your economic activity in the bailey and get rich. If an enemy approached, you would retreat to the motte and rain down arrows on the enemy until they gave up and went away. Then you would go back to the bailey, which is the place you wanted to be all along.
So the motte-and-bailey doctrine is when you make a bold, controversial statement. Then when somebody challenges you, you claim you were just making an obvious, uncontroversial statement, so you are clearly right and they are silly for challenging you. Then when the argument is over you go back to making the bold, controversial statement.
To defend against it, don’t allow the distraction of switching the discussion from one thing to another, speak to the logical error being made when the defensible position is conflated with the perverted version. Some examples are included here, like saying “oh, God is love and nature” when you know they also think God sends lightning bolts to sinners.