Affirming the consequent
From RationalWiki
Affirming the consequent is a logical fallacy often used in the context of trying to establish guilt by association. It is named after the consequent in a conditional statement (Q in "if P, then Q").
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Forms of the argument
Propositional logic
- If P, then Q.
- Q.
- Therefore, P.
In formal terms, the fallacious argument is stated as
.
First-order logic
- If P is true of x, then Q is true of x.
- Q is true of x.
- Therefore, P is true of x.
In formal terms, the fallacious argument is stated as
.
Examples of the argument
Propositional form
- If it is sunny today, then I will go swimming.
- I will go swimming.
- Therefore, it is sunny today.
First-order form
- Fascists support a strong military.
- John Q. Warhawk supports a strong military.
- Therefore, John Q. Warhawk is a fascist.