# (Fallacy of the) Undistributed middle term

Describes an (invalid) syllogism, in which the *middle term* that is connecting the two premises is not used according to the rules of distributivity.

Example of a syllogism *undistributed middle*:

Someareanimalscats.

Alldogsare.animals

~~Therefore, all~~dogsarecats.

## Other names

*Non distributio medii**Non distributivi sed collectivi medii*

## Rules of distributivity

The distribution rules for syllogisms are summarized in the article on distributivity. The specific rule that is violated by this fallacy can be formulated as follows:

**Remember:** The *middle term*, which connects the two premises, must occur in a distributed position in *at least one* of the premises.

The following table gives an overview of the distributivity of the terms in the four categorical statement types:

Statement | Subject | Predicate | |
---|---|---|---|

A | All S are P | distributed | not distributed |

E | No S is P | distributed | distributed |

I | Some S are P | not distributed | not distributed |

O | Some S are not P | not distributed | distributed |

With regards to the example above, the premises therein are of the types **I** and **A**; The *middle term* (“animals”) appears in both cases in *undistributed* positions, therefore this form of a *syllogism* is not valid.

## See also

## Weitere Informationen

- Fallacy of the undistributed middle on
*Wikipedia* - Fallacy of (the) Undistributed Middle on
*Logically Fallacious* - Undistributed Middle Term on
*Fallacy Files*