Illicit Major

Disciplines > Argument > Fallacies > x

Description | Discussion | Example | See also

Description

All X is Y. No P (which is a subset of Y) is X. Therefore no P is Y.

Unspoken assumption: All Y is X.

Example

All Londoners are European. No Parisiens are Londoners. Therefore no Parisiens are European.

Discussion

This is a particular case of a categorical syllogism, where overlaps of sets are taken to be different in each statement. Thus the fallacy in the example occurs when the first statement is assumed to be reversible (that if all Londoners are European, then all Europeans are Londoners).

More formally, the predicate (Y) of the conclusion (no P is Y) refers to all members of that set. Yet the same term (Y) in the major premise (All X is Y) refers only to some of the members (X) of that set.

The 'Major' in the name is the major premise, the first statement in the syllogism.

Classification

Assumptive, Syllogistic