Illicit major


 
Name of fallacy Illicit major
Aliases  
Type Deductive Argument, Formal Argument
Description A categorical syllogism that is invalid because its major term is undistributed in the major premise but distributed in the conclusion.
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.
Form 
Treatment This is an error in formal logic and dealt with by showing the error. For 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 linking object between the first and second premise is dogs. There is no statement about mammals and cats in the two premises. Just because no cats are dogs it does not follow that no cats are mammals.

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

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