Affirming the consequent
Affirming the consequent, sometimes called
converse error or
fallacy of the converse, is a formal fallacy of inferring the converse from the original statement. The corresponding argument has the general form: ▪ If
P, then
Q. ▪
Q. ▪ Therefore,
P. An argument of this form is invalid, i.e., the conclusion can be false even when statements 1 and 2 are true. Since
P was never asserted as the
only sufficient condition for
Q, other factors could account for
Q. To put it differently, if
P implies
Q, the
only inference that can be made is
non-Q implies
non-P. This is known as logical contraposition. Symbolically: The name
affirming the consequent derives from the premise
Q, which affirms the "then" clause of the conditional premise.