# Fallacy of Every and All

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## Fallacy

A statement containing both universal quantifiers and existential quantifiers has a different meaning if the order of the quantifiers is reversed.

To not recognize such a shift in meaning is to commit the **Fallacy of Every and All**.

## Counterexample

Let $x$ and $y$ be natural numbers.

- $\forall x \, \exists y : x = y$: for every $x$ there is some $y$ such that $x$ equals $y$.

Since $x = x$, this is true.

- $\exists y \, \forall x: x = y$: there is some $y$ such that for every $x$, $x$ equals $y$.

Since no natural number equals both $1$ and $2$ at the same time, this is false.

$\blacksquare$

## Sources

- 1995: Merrilee H. Salmon:
*Introduction to Logic and Critical Thinking*: $\S 11.5$, Appendix $B$: Every and All