A field guide to the ways reasoning breaks
Broken structure
Also called Shared trait fallacy
Concluding that two things are the same because they share one property.
All engineers use laptops; he uses a laptop, so he is an engineer.
Ask whether the shared property belongs only to the group in question.
Latin: non distributio medii — 'the middle is not distributed.' In a categorical syllogism the middle term is the hinge that links the two premises; if neither premise applies it to all of its class, the two halves of the argument may be touching different members of that class and never actually meet. Classified by Aristotle in the Prior Analytics and catalogued as a syllogistic fallacy ever since.
All committed employees answer late-night messages; Sam answers late-night messages; so Sam is committed.
Every toxic manager reduces team output; this team has low output; so their manager is toxic.
All great chefs love their work; he loves his work; so he's a great chef.
Every successful startup raised venture capital; this startup raised venture capital; so it will succeed.