Many common logical errors, including the fallacy of affirming the consequent, arise from the confusion of a statement with either its converse or its inverse.

A: I say that if Jumbo is an elephant, then he must be a mammal.

B: Don't be silly. I'm a mammal, and I'm certainly no elephant.

A bases his assertion on the correct premise: "If an animal is an elephant, then it is a mammal." B attempts to dispute the argument by affirming the consequent ("I'm a mammal"). In effect, he confuses A's premise with its converse, which is of course false: "If an animal is a mammal, then it must be an elephant."

C:	If a being is human, then it must be a mammal.
D:	Well, Fido isn't human, so you must think he isn't a mammal.

D confuses C's statement with its inverse. He thinks that C is saying: "If a being is not human, then it is not a mammal."

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A:	I say that if Jumbo is an elephant, then he must be a mammal.
B:	Don't be silly. I'm a mammal, and I'm certainly no elephant.