Illicit major

Illicit major is a formal fallacy committed in a categorical syllogism that is invalid because its major term is undistributed in the major premise but distributed in the conclusion.

This fallacy has the following argument form:

All A are B
No C are A
Therefore, no C are B

Example:

All dogs are mammals
No cats are dogs
Therefore, no cats are mammals

In this argument, the major term is "mammals". This is distributed in the conclusion (the last statement) because we are making a claim about a property of all mammals: that they are not cats. However, it is not distributed in the major premise (the first statement) where we are only talking about a property of some mammals: Only some mammals are dogs.

The error is in assuming that the converse of the first statement (that all mammals are dogs) is also true.

However, an argument in the following form differs from the above, and is valid (Camestres):

All A are B
No B are C
Therefore, no C are A

External links

Illicit Major The Fallacy Files

This article was originally based on material from the Free On-line Dictionary of Philosophy, which is licensed under the GFDL.

Formal fallacies

Masked man fallacy

In propositional logic	Affirming a disjunct Affirming the consequent Denying the antecedent Argument from fallacy False dilemma

In quantificational logic	Existential fallacy Illicit conversion Proof by example Quantifier shift

Syllogistic fallacy	Affirmative conclusion from a negative premise Exclusive premises Existential Necessity Four-term fallacy Illicit major Illicit minor Negative conclusion from affirmative premises Undistributed middle

Other types of formal fallacy List of fallacies

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Illicit major

See also

External links