When the meaning of a word or phrase changes within an argument in order to conceal the reasonableness of the conclusion, it becomes a fallacy of equivocation. The ambiguous use of terms in an argument can make it possible for a word to mean one thing within a statement of reason and something entirely different within the conclusion. This fallacy only occurs when a word or phrase uses two distinct meanings within an argument as a means of making the argument more persuasive (that is, to make it appear reasonable when in fact it is unreasonable). Be careful of arguments that lead you to assume one meaning of a word or phrase, when another meaning is intended.
Example Argument: “Noisy children are a real pain. Two aspirin will make any pain go away. Therefore, two aspirin will make noisy children go away.”
Premise 1: Noisy children are a pain.
Premise 2: Two aspirin will make any pain go away.
Conclusion: Two aspirin will make noisy children go away.
In this argument, the use of “pain” are used differently in the two premises. This misuse of terms makes the argument unreasonable, because premise one and premise two really do not have the right “pain” in common in order to establish the stated conclusion.