The term “motte and bailey” originates from the fortifications of medieval castles. A motte (a raised mound) provided a strong, defensible position, while a bailey (an enclosed courtyard) offered more accessible but less defensible space.
The motte and bailey fallacy is named after this castle design because, like the tactic of switching between an easily defensible position (the motte) and a more vulnerable but easier to access position (the bailey), it involves switching between extreme and moderate positions in an argument.