The Masked Man Fallacy: Where Knowledge isn’t Everything [#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 Masked Man 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.
The Origin of the Masked Man Fallacy
Based on what I read in the Oxford Dictionary of Philosophy, the famous French philosopher, Descartes, allegedly committed this fallacy. The story goes that he said that “since he can know things about his mind while not knowing them about his body, his mind cannot be identical with his body.” Broken down into a syllogism, his argument could look like this:
I can know things about my mind
I cannot know things about my body
Therefore, my mind cannot be identical to my body
[Fun fact: Descartes reasoning here is most notable in his work called Meditations of First Philosophy in which he makes the distinction between mind and body (aka dualism).]
Anyway, people that claim that Descartes made the masked man fallacy compare it to this syllogism:
I know who my father is
I don’t know who the masked man is
Therefore, the masked man cannot be my father
And it is this reasoning that gave birth to the name “Masked Man” fallacy.
What is the Masked Man Fallacy?
Well let’s revisit the “masked man” syllogism:
I know who my father is
I don’t know who the masked man is
Therefore, the masked man cannot be my father
The first two premises (“I know who my father is” and “I don’t know who the masked man is“) could very well be true. But there is also a good chance that the conclusion (“Therefore, the masked man cannot be my father“) is false. There is no way for the speaker to know until the man removes the mask.
The masked man fallacy (also known as the epistemic fallacy, the intensional fallacy, illicit substitution of identicals, and the hooded man fallacy) occurs when you assume that someone’s knowledge of something means that they know all possibilities of that thing.
So back to the masked man syllogism. Since the speaker knows who the father is, the speaker assumes that the father will show up only in instances where the speaker can recognize the father. But, of course, the masked man could very well be the father without the speaker’s knowledge.
This is why the masked man fallacy is also seen as an epistemic fallacy (or a knowledge-based fallacy). It assumes that there is no difference between the person's knowledge and the reality of the subject in question. Click To TweetThe Masked Man Fallacy and Leibniz’s Law
The Masked Man fallacy is also a misapplication of Leibniz’s law (also known as the Identity of Indiscernibles).
To see how this principle works, let’s say we have two things. We’ll call them x and y. If x and y are the same thing, then that means that they have the exact same properties. If there is any different trait between x and y, then they cannot be the same thing.
So using our masked man syllogism again, the speaker sees knowledge as the different “trait” between the father and the masked man; the speaker knows their father but does not know the masked man. Therefore, the speaker concludes that the father and masked man are not the same person.
However, someone’s knowledge is not a property or trait. It functions independently of the subject in question.
Intension vs. Extension
Earlier when I mentioned the definition of the masked man fallacy, you may have noticed all the alternative names for the masked man fallacy. One of them is the “intensional fallacy.” That name stems from the word “intension” that is often used in logic, math, and philosophy. Understanding this term (and how it contrasts to an extension) will give more insight into how the masked man fallacy works.
Intensions are the traits or characteristics implied by a word or term. For example, the intensions of the “laptop” include characteristics like “contains a screen,” “contains a keyboard,” “technological device” etc.
Extensions, on the other hand, are words or terms that represents how that object of interest can be applied. For example, extensions of “laptop” include Macbook Air laptops, Dell laptops, and all other laptops that have existed and will exist in the future.
Here’s another example: one of Iron Man’s intensions is “Iron-clad superhero.” An extension of Iron Man is Tony Stark. So if Iron Man can fly, that also means that Tony Stark can fly.
However, not everyone knows that Tony Stark and Iron Man are the same person. So if I say “Person A knows Iron Man flies” that does not necessarily mean that “Person A knows Tony Stark flies.” Person A may not know that Iron Man and Tony Stark (the extension) are the same person while knowing that Iron Man is an iron-clad superhero (the intension). So merely substituting “Iron Man” with “Tony Stark” may not accurately depict the person’s knowledge.
The masked man fallacy is aptly called the intensional fallacy because merely knowing something’s intensions does not equal knowing its extensions. As shown in the Tony Stark/Iron Man examples, they can’t be merely substituted.
More Syllogistic Examples
I know avocados are nutritious
I don’t know if guacamole is nutritious
Therefore, guacamole cannot be an avocado product
Just as it was shown in the masked man syllogism earlier, the person’s knowledge of something or someone is not necessarily the same as all the ways a thing can exist. Just because someone does not know if guacamole is nutritious does not mean that it cannot be an avocado product. (In this case, it turns out that yes, guacamole is, in fact, mashed up avocado.)
Katie thinks Lorraine is funny.
Katie saw a female comedy performer get booed off of the stage
Therefore, that person that got booed off of the stage could not be Lorraine.
Again, Katie’s knowledge (or, in this case, what she thinks) about Lorraine does not necessarily represent all the possibilities in which Lorraine can exist. Katie can find Lorraine funny while the crowd boos her off of the stage.
Moral of the story: Something being a certain way is not the same thing as knowing or thinking it is a certain way.
Quiz Time!
Now that you’ve learned what the masked man fallacy is, here’s a quiz to test your understanding. Which one of the following answer choices contains the masked man fallacy?
A. Justine is singing loudly. Katie turned down Justine’s mic as she was singing. Therefore, the room is now quieter as Justine is singing.
B. A is C. B is not C. Therefore, A is not B.
C. John knows Hugo is Haitian. John does not know if Hugo is Caribbean. Therefore, Hugo is not Caribbean.
D. Unica is talented. When she performed on stage, the crowd gave her a standing ovation. Standing ovations are only for performances that really move an audience. Therefore, it is likely that the crowd really loved her performance.
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