A field guide to the ways reasoning breaks
Broken structure
Also called Syntactic ambiguity
Drawing a conclusion from a sentence whose grammar allows more than one reading.
The sign said no parking on the grass, so parking on the road is banned too.
Rewrite the sentence in each possible reading and see which one was intended.
From the Greek amphibolía, 'double throw'. Aristotle treated it in the Sophistical Refutations as ambiguity arising from how words combine, not how they are defined. Modern grammarians renamed it structural or syntactic ambiguity; logicians kept the older name.
The memo said 'managers should review contractors weekly' — read as reviewing the contracts, or reviewing the people, and two departments walked away with opposite tasks.
A headline reports 'Police stop drivers leaving airport early' — leaving early, or leaving the airport? The comment section splits on the grammar, not the facts.
The landlord tells tenants 'pets under ten kilograms are fine', and a dispute follows over whether it is the weight or the number of pets.
A coach texts 'let's meet Tuesday after practice people' — one comma's absence schedules a meeting with half the team.