Equivocation is when a word shifts meaning in an argument.
1) Hot dogs are better than nothing. Nothing is better than Hamburgers. Therefore, hot dogs are better than hamburgers.
This is a popular example, and I do not know the original source. Notice how "nothing" means "no thing" in the first premise, but it means "all things" in the second premise.
2) Feathers are light. What is light cannot be dark. Therefore, feathers are not dark.
Notice how “light” refers to weight in the first sentence, but to color in the second.
3) I cannot freely break the speed limit or fly to the moon. Therefore, I do not have free will.
Notice “free” is being used in two different senses. In the first sentence, “free” means the “ability to do anything.” In the conclusion, “free” means “the ability to sometimes act other than I did.”
4) Something must be done. This bill is something. So this bill must be done (unknown origin).
Notice “something” can mean “an effective solution” or “any solution.”
5) Everyone is selfish because everyone always seeks pleasure.
Notice “selfish” is ambiguous because it can mean “seeking pleasure” or “what you seek pleasure in” (i.e. the object of pleasure).
Equivocation is probably the most common fallacy of ambiguity, but there are others: amphiboly, accent, composition, and division.
There are many ambiguous words in philosophy (e.g. free, God, knowledge), which leads to the equivocation fallacy... and discussions in which people talk past each other.
How to avoid
Precisely define your words and use the same meaning throughout the argument.
- Create or find humorous examples of ambiguity in the media.
Answers will vary:
Mother of Eight Makes a Hole in One.
Dean appears with his wife, Jimmy Carter.
Kids make nutritious snacks.