The fallacy of affirming the consequent Although evidence may be consistent with an initial proposition it might be equally consistent with a range of alternative propositions. Too often people do not even think of the alternative hypotheses and simply conclude that since the evidence is consistent with their theory then the theory is true. This form of reasoning commits the logical fallacy of affirming the consequent. This form of reasoning has the following logical structure:
If A is true then B should follow.
We observe B.
Therefore A is true.