Illicit major

Illicit major is a logical 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.

See also

• Illicit minor
• Syllogistic fallacy

External links

• Illicit Major The Fallacy Files

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