Illicit Contraposition (aka “Flipped Negations”) [#FallacyFridays]
Welcome to #FallacyFridays! Though these posts are posted every Friday, any day is a good day to learn about the flaws in our logic that we should try to avoid making. Today’s logical fallacy is the illicit contraposition fallacy. Make sure to read all the way to the end so you can take the quiz that tests your understanding of the fallacy. 🤓
But before we get into it, I want you to know about a tool that may help you understand this and other fallacies. I know that some people learn better by writing or typing. If that is you, download this FREE digital copy of “#FallacyFridays: The Workbook.” It was designed to follow alongside #FallacyFridays lessons in order for you to better understand logical fallacies.
What is the Illicit Contraposition Fallacy?
If you are familiar with this corner of cyberspace, you may have been here when I covered the illicit conversion fallacy. One of the patterns of the fallacy looks like the following:
Some X are Y
Therefore, some Y are X.
Now if we made this look like the illicit contraposition fallacy, it would look like this:
Some X are Y
Therefore, some non-Y are non-X.
The illicit conversion and illicit contraposition fallacies both work when the terms switch places. The terms here are X and Y.
In the first half of both fallacies, X is the subject. And the latter half, X is the predicate.
In the first half of both fallacies, Y is the predicate. And in the latter half, Y is the subject.
Check out the fallacies side-by-side and note the position of the X and Y to see what I’m talking about. The illicit conversion fallacy is on the left and the illicit contraposition (today’s fallacy) is on the right:
Some X are Y
Therefore, some Y are X.
Some X are Y
Therefore, some non-Y are non-X.
Even though the premise for both fallacies are the same (“Some X are Y”), you probably see the big difference between the two fallacies: the fact that we have “non-” in front of the X and Y terms in the conclusion of the illicit contraposition fallacy. In other words, this flawed pattern of logic is saying that if some of X is part of Y, some of the negation of Y (“non-Y”) is the negation of X (“non-X”).
The same thing applies to illicit contraposition fallacies that involve the word “No” as follows:
No X are Y
Therefore, no non-Y are non-X.
The illicit contraposition fallacy occurs when we take the subject and predicate in the premise (X are Y) and have them switch places in the conclusion while negating them (non-Y are non-X). The fallacies use the determiners “no” or “some.”
The illicit contraposition fallacy follows the following pattern: "Some/No X are Y. Therefore, some/no non-Y are non-X." Click To Tweet💡Key Point: The illicit contraposition fallacy is fallacious due to the pattern or form of logic used. That is why it is classified as a “formal fallacy.”
Examples of the Illicit Conversion Fallacies.
Some technology includes Apple products. Therefore, non-Apple products are non-technology.
No nerds are social people. Therefore, no non-social people are non-nerds.
Some artists are sculptors. Therefore, some non-sculptors are non-artists.
No houses are apartments. Therefore, no non-apartments are non-houses.
💡Key Point: All of these examples are illicit conversion fallacies because they assume that you can always take the inverse of the premise and negate it in order to come to a valid conclusion. But as we can see, that is not true.
Illicit contraposition fallacies are fallacious because they conclude that you can take the inverse of the premise and negate its terms in order to come to a valid conclusion. Click To TweetQuiz Time!
Now that you’ve learned what the illicit contraposition fallacy is, here’s a quiz to test your understanding. Which one of the following answer choices contains the illicit contraposition fallacy?
A. All dogs are animals. Therefore all non-animals are non-dogs.
B. No humans are monkeys. Therefore, no non-monkeys are non-humans.
C. Some travellers are ignorant people. Therefore, some non-travellers are non-ignorant people.
D. No sins are good ethical decisions. Therefore, no non-sins are non-good ethical.
Input your answer choice below! 👇🏾
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