# Undistributed middle

*Also called: Shared trait fallacy*

- **Cluster:** Broken structure — The form itself does not carry the conclusion
- **Page:** https://fallacy.wiki/fallacy/undistributed-middle/
- **In Arabic:** https://fallacy.wiki/ar/fallacy/undistributed-middle.md
- **Licence:** CC BY 4.0 — https://creativecommons.org/licenses/by/4.0/

## What it is

Concluding that two things are the same because they share one property.

## In the wild

> All engineers use laptops; he uses a laptop, so he is an engineer.

## How to answer it

Ask whether the shared property belongs only to the group in question.

## Origin and naming

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.

## More places it shows up

- 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.

## How to spot it

- Notice when the two halves of the argument both point at the same trait but each could be looking at a different group.
- Notice when the conclusion pins one person to a category via a property that half the world shares.
- Notice when the premises say 'all As have trait T' and 'this has trait T' — and the conclusion forgets other things have T too.

## Nearby

- [Illicit major](https://fallacy.wiki/fallacy/illicit-major.md)
- [Affirming the consequent](https://fallacy.wiki/fallacy/affirming-consequent.md)
- [Fallacy of composition](https://fallacy.wiki/fallacy/composition.md)
- [Existential fallacy](https://fallacy.wiki/fallacy/existential.md)

## Read more

- [Wikipedia](https://en.wikipedia.org/wiki/Fallacy_of_the_undistributed_middle)
- [Internet Encyclopedia of Philosophy](https://iep.utm.edu/fallacy/)

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From fallacy.wiki — a bilingual field guide to 91 logical fallacies, published by phi holdings. Licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/): reuse freely with attribution to fallacy.wiki.