Motte-and-bailey fallacy

Core claim: Two different positions – one is a strong claim but vulnerable to attacks (the “bailey”) and the other is a weak claim but easily defensible (the “motte”) – are conflated under a single ambiguous term, so that arguments for or against one are treated as if they applied to the other.

• A single term is used to cover two distinct claims of different strength or scope: one of them is a strong, but difficult to defend claim (the “bailey”) and the other a weak but easily defended claim (the “motte”).
• When the “bailey”-position is attacked, the speaker retreats to the weaker but defensible “motte” position, while continuing to argue as if the original claim is still being defended.
• Arguments for one position are presented as support (or refutation) of the other, without acknowledging that the two positions differ in important respects.
• Reversed form: an opponent claims that a successful attack on the vulnerable “bailey” position automatically defeats the more defensible “motte” position as well.

• A speaker retreats from their original strong claim and proceeds to defend the weaker claim without trying to conflate the two positions (honest revision during discussion).
• The term has one consistent meaning in the discussion and both parties use it identically.
• The discussion is about defining or clarifying terminology itself without transferring arguments between different positions.

• Equivocation – ask: does a single word shift meaning within an argument (→ equivocation), or are two distinct positions/claims conflated under one label and defended as if identical (→ motte-and-bailey)?
• Straw man – ask: is someone misrepresenting a position to attack it more easily (→ straw man), or are they retreating from an attacked claim to a different but related defensible claim while pretending they’re the same (→ motte-and-bailey)? The two often occur together.
• Mereological fallacy – ask: is the error about transferring properties between parts and wholes of one system (→ mereological), or about conflating two distinct positions under one term (→ motte-and-bailey)?

Input: “Homeopathy should not be so easily dismissed, because naturopathy is a recognized medical discipline with proven successful treatments!”
Output: Homeopathy and naturopathy are two different fields. The merits of naturopathy do not tell us anything about homeopathy, neither in the positive nor in the negative sense. They both should be evaluated separately, on their own evidence.

Input: “The blockchain is cryptographically secure, so this exchange’s trading platform must be safe too.”
Output: The tamper-proof data structure (motte) does not make the surrounding implementation – distribution code, exchanges, mining platforms (bailey) – equally secure. Evaluate each component’s security separately instead of transferring trust from one to the other.

Input: “If you can’t show this statement corresponds to reality, then it isn’t true.”
Output: This silently swaps definitions of truth: attacking one notion of truth (e.g., correspondence) does not defeat another (e.g., coherence or consensus). State which definition of “truth” is at stake and argue within that framework.

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