A field guide to the ways reasoning breaks
Broken structure
Also called Persuasive definition
Defining a contested term in a way that settles the dispute by wording alone.
Good just means whatever I prefer, so my view is good by definition.
Offer a neutral definition both sides would accept before arguing.
Charles Stevenson coined 'persuasive definition' in his 1938 paper of the same name, part of his work on the emotive meaning of ethical terms. The definist fallacy is the argumentative move built on it: smuggling a verdict into a definition so the debate is over before it starts.
In a performance review dispute, one side defines 'productivity' as lines of code written — and suddenly one engineer is top of the team by definition.
A lobby group defines 'family-friendly content' as content they approve of, then campaigns against everything else as anti-family.
A founder defines 'traction' as whatever metric their startup happens to be growing, and declares the company successful.
In a policy debate, 'reform' is defined as the speaker's own proposal, so any objection is an objection to reform.