Fallacy of the Undistributed Middle | Categories and Groups | Evidentia

Fallacy of the Undistributed Middle

F011 • Formal - Syllogistic Logic

Also known as: Undistributed Middle Term

Difficulty 1/10Low-Medium LoadCommon

Definition

A categorical syllogism where the middle term is not distributed in at least one premise.

Why Invalid

The middle term must connect the major and minor terms, but if it's not distributed, it doesn't establish the necessary connection.

Examples

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Scope of Applicability

Identify the three-term categorical syllogism
Identify the middle term (appears in both premises)
Check if middle term is distributed in at least one premise
A term is distributed if the statement makes a claim about all members of that category

Common Mistakes

Not understanding distribution rules
Confusing with valid syllogistic forms

Illicit MajorIllicit Minor

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F012 Illicit Major

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