(Semantics, Splitting Hairs, Playing With Words, or Using Legalisms, Fallacy of Equivocation, Doublespeak)
This fallacy occurs when someone uses the inherent ambiguity in a word to manipulate the audience by suggesting that a word means something that it doesn’t, often by allowing the meaning of a word to change during the argument and thus invalidating the conclusion. Equivocations are common in the American legal system, newspaper headlines, and anti-science arguments. They are also very effective in humor and satire.
This is very often part of an appeal to emotion; many words have strong emotional connotations, and by suggesting an incorrect meaning, the arguer is manipulating the audience into reacting emotionally based on the meaning that they are implying.
To prevent committing this fallacy, make sure that the definition you are using for the word doesn’t change throughout the argument, and if you suspect someone is using this fallacy, replace each usage of the word with the same definition to see if it still makes sense.
Examples:
“Really exciting novels are rare. Rare books are expensive. Therefore, really exciting novels are expensive.”
Bill Clinton stated repeated that “I did not have sexual relations with that woman,” knowing full well that “sexual relations” has two different meanings. He was guilty under one meaning, not guilty under the other.
“No man of woman born can kill Macbeth.” (Macduff, who does kill Macbeth, was caesarian).
“Only man is rational. No woman is a man. Therefore, no woman is rational.”
“No one who has the slightest acquaintance with science can reasonably doubt that the miracles in the Bible actually took place. Every year we witness countless new miracles in the form recombinant DNA, micro-chips, organ transplants, and the like.” (The word “miracle” does not have the same meaning in each case)
“People testing for faster than light phenomena must not know it’s impossible to travel faster than the speed of light.” (Under our current understanding of relativity, it is impossible. However, that doesn’t mean that our current understanding is complete and that we may one day discover how.)
“Margarine is better than nothing. Nothing is better than butter. Therefore, margarine is better than butter.” (Similarly, “A warm beer is better than a cold beer. After all, nothing is better than a cold beer, and a warm beer is better than nothing.”)
“The laws imply lawgivers. There are laws in nature. Therefore there must be a cosmic lawgiver.”
“Noisy children are a real headache. Two aspirin will make a headache go away. Therefore, two aspirin will make noisy children go away.”
“I don’t see how you can say you’re an ethical person. It’s so hard to get you to do anything; your work ethic is so bad.”
“Philosophy is supposed to stand on neutral ground. But most philosophers argue for very definite conclusions. This is hardly standing on neutral ground. Shouldn’t we conclude that most philosophers aren’t doing philosophy?”
“Sarah was put in classes for the exceptional student. But I discovered that despite her age she could hardly read. Surely she was put in these classes by error.”
“The sign said ‘fine for parking here,’ and since it was fine, I parked there.”
“All child-murderers are inhuman, thus, no child-murderer is human.” (From Barker, p. 164; this is called “illicit obversion”)
“I want to have myself a merry little Christmas, but I refuse to do as the song suggests and make the yuletide gay. I don’t think sexual preference should have anything to do with enjoying the holiday.”
“The priest told me I should have faith. I have faith that my son will do well in school this year. Therefore, the priest should be happy with me.” (The term “faith” has two different meanings. As the priest uses it, faith means believing without sufficient evidence; As the father uses it, it means “confidence” based on evidence and experience). (Similarly, “You have faith in science, and I have faith in God.”)
“Because it’s called the theory of evolution, evolution is an unproven assumption!” (The word “theory” has two different meanings, and the scientific version of the word incorporates all known facts and laws).
“Because the word ‘Nazi’ is short for ‘National Socialism,’ socialists are Nazis.” (In different countries and at different times, terms used by political parties to identify themselves have changed. The modern “Liberal Party of Australia” are in no way similar to liberals in America.)
“The theory of relativity is immoral because it promotes moral relativism.”
“Since evolutionism is based on the work of Darwin, evolutionists are in favor of Social Darwinism.” (Social Darwinism, while named after Darwin, was not supported by him, nor is it even supported by modern evolutionary theory.)
“People who agitate for income equality, marriage equality, and gender equality are doomed because individual humans don’t have equal abilities.” (Equality of ability is irrelevant to equality under the law.)