|Part of the series on|
“”Marriage is a fine institution, but I'm not ready for an institution.
|—Mae West, The 2,548 Best Things Anybody Ever Said|
Equivocation is a logical fallacy that relies on implicitly alternating between the different meanings a single word can have in different contexts.
When the switch is purposefully made obvious, the result is often humorous (see above quote). When the switch is done as quietly as possible, however, the result becomes misleading instead.
It is a favorite fallacy of creationist and woo hucksters alike. It can be used both to seemingly belittle a concept or idea, or to raise one up to false pretenses. It can be used to disguise bullshit like in quantum woo where people like Deepak Chopra use equivocation to make their ideas sound like they have some basis in reality.
P1: X is Y (meaning 1).
P2: Y (meaning 2) is Z.
C1: X is Z.
With letters representing words, this may seem obviously false, but when words are introduced, the fallacy becomes much less apparent.
 Obviously false
P1: Noisy children are real headaches.
P2: An aspirin makes real headaches go away.
C1: An aspirin will make noisy children go away.
P1: Nothing is better than eternal happiness.
P2: A ham sandwich is better than nothing.
C1: A ham sandwich is better than eternal happiness.
P1: All bark is grown on trees.
P2: All dogs bark.
C1: All dogs are trees.
P1: 1 is a number.
P2: 2 is a number.
C1: 1 is 2.
In this case, the word "is" in the two premises is used differently in meaning than "is equivalent to" in the conclusion
 Less obvious
- "Because it's called the theory of evolution, evolution is an unproven assumption!"
- This is fallacious because it equivocates two different meanings of the word "theory."
- "You have faith in science, and I have faith in God."
- This exploits the fact that "faith" is often used to mean "confidence," that is having a solid reason to be confident of something due to its past performance—this argument is an effort to equate science with religion, when in reality science does not require faith (meaning belief without evidence).
- "The theory of relativity is immoral because it promotes moral relativism."
- This equivocates two different meanings of the word "relative."
 See also
- Fallacy of ambiguity
- Fallacy of accent
- Fallacy of amphiboly
- Illicit observation
- Quote mining
- Rationalist taboo