Motte-and-bailey fallacy

Informal fallacy

The motte-and-bailey fallacy is a way of arguing where someone uses two different ideas that seem similar but are not the same.

One idea (the "motte") is easy to defend either because its self evident, vague or not very controversial.

The other idea (the "bailey") is more controversial and harder to defend.

The speaker wants to assert the Bailey, the hard position to defend. However, when challenged, the speaker retreats from the bailey to the motte, but later returns to the bailey when the pressure is off, without acknowledging the shift.