Illicit Conversion: The Converse Scenario Isn’t Always True [#FallacyFridays]
Welcome to #FallacyFridays! Fridays are all about looking at logical fallacies so we know which types of arguments to avoid making. Today’s fallacy is called the illicit conversion 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 an Illicit Conversion Fallacy? And how Does it Work?
Let’s say someone says the following:
All dogs are four-legged animals. Therefore, all four-legged animals are dogs.
You probably see what’s wrong here, right? While the first statement is true (at least in nearly all cases), the second statement (Therefore, all four-legged animals are dogs) is not true. There are zebras, cats, tigers, and plenty other four-legged creatures.
You also probably notice the pattern in the way this example was written too. “Dogs” and “four-legged animals” switched places. While “dogs” was the subject in the first statement (“All dogs are four-legged animals“), it become the predicate in the second statement (“…all four-legged animals are dogs.“). Similarly, “four legged animals” was in the predicate of the first statement (“All dogs are four-legged animals“) and became the subject in the second statement (“…all four-legged animals are dogs.“). So from here, you can see how the subject and predicate switch places in illicit conversions.
You can see the switching pattern in this form:
All X is Y
Therefore, all Y is X.
You can also see how the word “all” (as seen in “all dogs” and “all four-legged animals”) comes before each subject. “All”–just like the words “some,” “no,” and “none”–are quantifiable determiners. Basically, this means that let us know how much of something is being considered. And these determiners are used in illicit conversions.
Categorical Terms and Categorical Propositions
Continuing with the example up top, we saw that they contained the following statements:
All dogs are four-legged animals.
All four-legged animals are dogs.
The parts in bold are categorical terms. They let us know how terms like “dogs” and “four-legged animals” are being categorized. In this case, all dogs and all four-legged animals are being considered in these statements.
In addition, both of the above statements are called categorical propositions. A categorical proposition lets you know the relationship between categories: if they are fully contained, partially contained, or completely separate from each other.
So the categorical proposition “all dogs are four-legged animals” is claiming that the categorical term “dogs” is fully contained within the the categorical term “four-legged animals” since it starts off with the determiner “all.”
Likewise, the categorical proposition “all four-legged animals are dogs” is claiming that the term “four-legged animals” is fully contained within the the categorical term “dogs” since it also starts off with the determiner “all.”
So fully contained terms start off with “all.”
Partially contained terms start off with “some”
And terms that start off with “no” or “none of” are not contained at all.
From the example and its analysis, we can now adequately determine what an illicit conversion is.
An illicit conversion occurs when one switches the subject and predicate from a categorical proposition in order to come to conclusion in another categorical proposition. The two propositions are converse to each other.
The illicit conversion fallacy makes the mistake of assuming that the converse of a categorical proposition is true. For example, just because all dogs are four-legged animals does not mean that all four-legged animals are dogs. Click To TweetTypes of Categorical Propositions and Illicit Conversions
There are four types of categorical propositions: Types A, E, I, and O.
As already stated, the above illicit conversion example used the word “all.” When illicit conversions include categorical propositions with the word “all,” they are invalid and contain categorical propositions that are “Type A.”
A categorical proposition can have the word “no.” This can be seen in this illicit conversion example: “No basketballs are oblong-shaped balls. Therefore, no oblong-shaped balls are basketballs.” As you might have noticed, this conversion is valid. And the categorical propositions in the conversion are “Type E.”
A categorical proposition can have the word “some.” This can be seen in this illicit conversion example: “Some men are tall people. Therefore, some tall people are men.” This conversion is also valid. And the categorical propositions in the conversion are “Type I.”
The word “some” can also be applied to the in this illicit conversion example: “Some men are not tall people. Therefore, some tall people are not men.” With that “not” in the categorical propositions, this invalid conversion is called “Type O.”
Some More Examples of the Illicit Conversion Fallacy
All people named Tina are girls. Therefore all girls are named Tina.
No housecat does not meow. Therefore, no meowing means it’s not a housecat.
Some classes are bore me. Therefore, if I’m bored, I’m in some of those classes.
💡Key Point: Whether or not these syllogisms contains valid statements, it is still the illicit conversion fallacy at work because the statement isn’t always valid. It is not always valid his because of how the argument is structured: the flipping of the subject and predicate as I mentioned earlier.
The structure or form found in the illicit conversion fallacy is not a reliable means of making valid statements. That is what makes the illicit conversion fallacy a formal fallacy. Click To TweetQuiz Time!
Now that you’ve learned what the illicit conversion fallacy is, here’s a quiz to test your understanding. Which one of the following answer choices contains the illicit conversion fallacy?
A. All comedians are funny people. Therefore, all funny people are comedians.
B. Kings like beer. Therefore, beer is a king’s favorite.
C. Some trees are tall. Therefore, tall people can be likened to trees.
D. No one is without hypocrisy. Therefore, no one can point the finger at others and fault them for their mistakes.
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