# Existential fallacy

*Also called: Existential instantiation error*

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

## What it is

Concluding that something exists from premises that only describe a category conditionally.

## In the wild

> All unicorns are white, so some white things are unicorns.

## How to answer it

Ask whether any member of the category has been shown to exist.

## Origin and naming

A fallacy of the quantified syllogism: premises that only say every member of a class would have a property are read as proving that some member exists. Medieval logic assumed universal statements carried 'existential import'; Bertrand Russell's 1905 essay 'The Existential Import of Proposition' helped settle the modern, Boolean convention that they do not.

## More places it shows up

- All unicorn sightings in the data are fake; therefore some fake sightings are unicorn sightings — the set may simply be empty.
- Every overdue invoice gets a penalty fee; therefore some invoices have penalty fees — says the report whose penalty table has zero rows.
- All prohibited items are confiscated at the gate; so some items were confiscated today — on a day nothing was prohibited from entering.
- All ghost sightings happen at night; therefore some nighttime events are ghost sightings — before establishing a single sighting exists.

## How to spot it

- Notice when the conclusion says 'some exist' while every premise only says 'all, if any'.
- Notice when swapping the subject for something plainly fictional — dragons, unicorns — leaves the reasoning untouched.
- Notice when a database query returns zero rows and the argument still proceeds as if it returned some.

## Nearby

- [Illicit major](https://fallacy.wiki/fallacy/illicit-major.md)
- [Undistributed middle](https://fallacy.wiki/fallacy/undistributed-middle.md)

## Read more

- [Wikipedia](https://en.wikipedia.org/wiki/Existential_fallacy)
- [The Logic Museum](https://www.logicmuseum.com/wiki/Existential_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.