Tag Archives: affirming the consequent

Fallacy Files #3: Confused Conditionals

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One common logical fallacy is known as ‘affirming the consequent’. Arguments that commit this fallacy have this general form:

If P then Q.

Q.

Therefore P.

(In technical terminology, P is the antecedent of the first, conditional premise and Q is the consequent of that premise. The second premise of the argument affirms the consequent of the first premise rather than its antecedent; hence the fallacy of ‘affirming the consequent’.)

It isn’t difficult to see that such arguments are fallacious, as this example makes plain:

If Bob lives in Chicago then Bob lives in America.

Bob lives in America.

Therefore Bob lives in Chicago.

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