10. Equivocation
Wireless Philosophy, Fallacies, 6:30. Original title: CRITICAL THINKING - Fallacies: Equivocation [HD]
Summary
Joseph Wu (University of Cambridge) explains the informal fallacy of equivocation, which comes up all the time, beginning with a deliberately simple case:
Premise 1: All stars are exploding balls of gas.
Premise 2: Miley Cyrus is a star.
Conclusion: Therefore, Miley Cyrus is an exploding ball of gas.
The form looks valid, and each premise taken on its own is true. An argument with a valid form and true premises is sound, and a sound argument necessarily has a true conclusion. Yet nobody is convinced that Miley Cyrus is an exploding ball of gas, and rightly so, because the logic is flawed.
What has gone wrong
The word "star" carries different meanings in the two premises. In the first it means a celestial sphere of plasma; in the second it means a famous person. The premises equivocate between the two senses.
Equivocation occurs when the same word is used to express different meanings throughout an argument.
The arguer commits a fallacy by using the word as though its meaning were constant, which makes the argument appear valid when it is not. Equivocation grows out of ordinary ambiguity in language: many words carry more than one meaning, so we have to watch that key terms do not shift sense in the course of an argument.
The test: restate without the ambiguous term
Since the fallacy lives in a single ambiguous word, the way to expose it is to substitute the definitions back into the premises:
Premise 1: All celestial spheres of plasma are exploding balls of gas.
Premise 2: Miley Cyrus is a famous person.
Conclusion: Therefore, Miley Cyrus is an exploding ball of gas.
Both premises remain true, and the invalidity is now unmissable: the conclusion simply does not follow.
Two harder cases
A respectable newspaper is criticised for spreading celebrity gossip, and its editor replies:
Premise 1: Newspapers have a duty to print stories that are in the public interest.
Premise 2: The public has great interest in rumours about celebrities, since circulation increases when newspapers print such stories.
Conclusion: It's not wrong for respectable newspapers to pass on rumours about celebrities.
The key term is "interest". In the first premise it means the benefit of a person or group ("it is in your interest to keep your bank details private"); in the second it means an activity one enjoys ("my interests are swimming, hiking and reading"). The meaning has shifted, so the argument is not valid.
The second case comes from a friend: organic compounds contain carbon, and organic foods are better for the environment, so when grocery shopping you should look for foods that contain carbon, since those are better for the environment. The absurd conclusion is the alarm bell. "Organic compounds contain carbon" is true in the chemical sense of the word; "organic foods are better for the environment" is true in the agricultural sense, which refers to how food was produced and processed. Two meanings, so no valid argument.
Wu adds that even within the agricultural sense the threat of equivocation persists, because different countries set different standards for what counts as organic, different foods follow different standards, and labels in the United States range from products made with 100 percent organic ingredients down to products made with at least 70 percent.
Key takeaway
When you suspect equivocation, work through three steps: distinguish the possible meanings of the ambiguous term, restate the argument without that term so that the premises stay true, and then evaluate the result. If the restated argument is no longer valid, the original committed the fallacy of equivocation.