Steelman
Illicit minor
Also called illicit process of the minor term.
The conclusion generalizes about all of the subject when the premises only covered some.
What it is
A categorical syllogism whose minor term (the subject of the conclusion) is distributed in the conclusion but not in the premise where it appears.
The pattern
All M are P. All M are S. Therefore, all S are P. (invalid)
An example
“All squares are rectangles. All squares are rhombuses. Therefore, all rhombuses are rectangles.”
Both premises are true, but plenty of rhombuses (slanted diamond shapes) aren’t rectangles. Squares are only some of the rhombuses.
Why it fails
“All M are S” only tells us about the Ss that are Ms. The conclusion claims something about every S, including Ss the premises never mentioned.
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
- The conclusion is suitably limited: “Some S are P” does follow here (provided there is at least one M).
Try one
A question from the app. The wrong answers are its usual look-alikes.
Dad, flipping through his records: “Every album on this shelf is a classic. Every album on this shelf came out in the seventies. The seventies? Nothing but classics. That’s the decade your playlist is up against.”
What’s the flaw?
The shelf is a small, hand-picked slice of seventies music. The premises only describe that slice, but the conclusion covers every album from the decade, including the many forgettable ones that never made the shelf.
A fair reply
“Your shelf is the best of the seventies, not all of it; plenty of seventies albums are long forgotten.”
Often confused with
- Illicit major
Illicit major makes the same error with the conclusion’s predicate term.
- Hasty generalization
Hasty generalization is the inductive cousin: generalizing from part of a group to all of it on thin evidence.
Where the name comes from
The minor term is the group the conclusion is about, called its subject. In “Every student here is good at math,” it’s “every student here.” Illicit means not allowed. The conclusion makes a claim about all of that group, but its premise only covered some of it. Illicit process of the minor term is the longer, traditional name.
Sources
- Illicit Minor, The Fallacy Files
- Syllogistic Fallacy (terminology and distribution), The Fallacy Files
In the app
Practice spotting it on arguments that sound real.
Steelman has more examples of illicit minor, 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.
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