Steelman
Four terms
Also called quaternio terminorum, four-term fallacy, ambiguous middle.
A syllogism that sneaks in a fourth term, usually by using one word in two senses.
What it is
An argument shaped like a categorical syllogism that actually contains four distinct terms instead of three, so the premises never link the conclusion’s terms. The extra term is usually hidden by an equivocation.
The pattern
All A are B. All C are D. (B and C look alike but mean different things) Therefore, all A are D.
An example
“Every star is a huge ball of burning gas. My favorite actor is a star. So my favorite actor is a huge ball of burning gas.”
“Star” means a celestial body in the first premise and a celebrity in the second: four terms, not three.
Why it fails
A valid syllogism needs exactly three terms, each appearing twice with the same meaning. If the “shared” middle term changes meaning between premises, there’s no bridge between the other two.
When it’s not a fallacy
Most lists skip this part. Calling a fair point a fallacy is a mistake too.
It can be fair when
- Two different words are used for the same term (e.g. “lawyer” and “attorney”). A term is a meaning, not a word.
Try one
A question from the app. The wrong answers are its usual look-alikes.
Comment under a science video. Dale: “A theory is an idea nobody’s proven yet. That’s what the word means. And evolution is a theory; even your biology textbook calls it that. It’s an unproven idea, then, and schools should teach it as one.”
What’s the flaw?
“Theory” shifts meaning. In everyday talk it means a hunch; in science it means a well-tested explanation, the same word used for the theory of gravity. Since the shared word means two things, the two lines never connect.
A fair reply
“In science, ‘theory’ means a tested explanation, the same word they use for gravity.”
Often confused with
- Equivocation
Equivocation is the informal fallacy of shifting a word’s meaning. When it happens in a syllogism’s middle term, the result is four terms.
Where the name comes from
A syllogism is a two-premise argument that links three groups, called terms. Quaternio terminorum is Latin for “a set of four terms”: one word quietly means two things, so three terms become four. Four-term fallacy says the same in English. Ambiguous middle names where it usually happens: the middle term, the link between the premises, has two meanings.
Sources
- The Four Term Fallacy, The Fallacy Files
- Fallacies, Bradley Dowden, Internet Encyclopedia of Philosophy
In the app
Practice spotting it on arguments that sound real.
Steelman has more examples of four terms, how to answer it in a real conversation, and practice rounds that mix it with its look-alikes, so you learn the difference, not just the name. Coming soon to iPhone and Android.
You’re on the list.
We’ll email you the day Steelman is out.
Thanks for offering to test. We’ll write before the beta with how to join.