# Affirming a disjunct

*Also called: Inclusive or error*

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

## What it is

Assuming that because one option in an or statement is true, the other must be false.

## In the wild

> She is in sales or marketing; she is in sales, so she is not in marketing.

## How to answer it

Ask whether the or was meant as exclusive. Usually both can hold.

## Origin and naming

The name describes the move: one half of an 'or' statement is affirmed, and from that the other half is denied. The error comes from reading 'or' as exclusive — at most one option true — when ordinary usage is often inclusive, and both can hold at once.

## More places it shows up

- The outage was caused by the database or the cache; we confirmed the database, so the cache is fine.
- He is on leave for family reasons or burnout; HR confirmed family reasons, so it is not burnout.
- The delay came from the vendor or from our own approvals; the vendor was late, so our approvals are cleared.
- Users churn because of price or features; the survey says price, so the feature roadmap is not the problem.

## How to spot it

- Notice when 'or' is quietly being treated as 'exactly one of these,' with no argument for why.
- Notice when confirming one option is used to close the investigation instead of narrow it.
- Notice when both things being true would explain the evidence better than either alone.

## Nearby

- [False dilemma](https://fallacy.wiki/fallacy/false-dilemma.md)
- [Affirming the consequent](https://fallacy.wiki/fallacy/affirming-consequent.md)

## Read more

- [Wikipedia](https://en.wikipedia.org/wiki/Affirming_a_disjunct)
- [The Fallacy Files](https://www.fallacyfiles.org/afonedis.html)

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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.