A field guide to the ways reasoning breaks
Broken structure
Also called Quaternio terminorum
A syllogism that looks valid but uses four terms because one word shifted meaning.
Nothing is better than wisdom; a sandwich is better than nothing; so a sandwich beats wisdom.
Count the distinct concepts, not the distinct words. A valid syllogism has exactly three.
Quaternio terminorum — 'four terms' — names a syllogism that carries one term too many. A valid categorical syllogism needs exactly three: the two in the conclusion plus the middle that links them. In practice the fourth term is usually smuggled in by one word doing double duty, which makes this fallacy a close cousin of equivocation.
Banks deal with money; the river has banks; so the river deals with money.
Justice requires blind judgment; a referee is blind to the replay; so referees are just.
Stars light up the sky; celebrities are stars; so celebrities light up the sky.
Iron is an element; you iron a shirt; so pressing shirts involves chemistry homework.