Illicit Substitution of Identicals
Knowing that two names refer to the same person does not mean someone else recognizes that identity. Substituting those names inside a statement about what that person believes or knows can therefore produce a false conclusion.
THE IDEA
Illicit Substitution of Identicals
(also known as: hooded man fallacy, masked man fallacy, intensional fallacy)
Description: A person may recognize someone under one name without recognizing them under another. In an extensional statement about that person, two names for the same individual can be interchangeable. In an intensional context, such as a report of what someone believes or knows, that substitution may change the truth of the statement.
Imagine Superman, who is also Clark Kent, flew to Italy for a slice of pizza. If we said, “Clark Kent flew to Italy for pizza” we would be right, because of the extensional context of that statement. Conversely, if we said, “Lois Lane thinks Superman flew to Italy for pizza”, we would still be making a true claim, although the context is now intensional, as indicated by the term, “thinks”. Now if we said, “Lois Lane thinks Clark Kent flew to Italy for pizza”, we would be wrong and would have committed this fallacy, because Lois does not believe that, even though extensionally it is the case (this is after the kiss that wiped her memory of Clark being Superman).
Source gap: Example #1 and Example #2 are not included in the excerpt. Their accompanying explanation refers to a reporter who “thinks”, but the specific arguments are missing.
Substituting identicals in an extensional context can be valid under Leibniz’ Law. The excerpt refers to a valid version of example #1, but does not include it.
When to use it
In debates about personal identity, when assuming that because two descriptions refer to the same person, all beliefs about one apply to the other.
In marketing, when a company rebrands but consumers still hold attitudes about the old name, leading to incorrect inferences about brand perception.
In philosophy of mind, when discussing whether someone can know an object under one description but not another (e.g., the famous 'Superman/Clark Kent' puzzle).
In detective work, when a witness says 'I saw the murderer run away' but does not realize the murderer is their neighbor, leading to false assumptions about what they know.
FROM THEORY TO EVERYDAY LIFE
In practice
Lois Lane and the Identity of Superman
Lois Lane believes that Superman flew to Italy for pizza. She does not know that Superman is Clark Kent. If someone argues, 'Clark Kent is Superman, and Lois thinks Superman flew to Italy, therefore Lois thinks Clark Kent flew to Italy,' this commits the fallacy. The intensional context ('thinks') prevents substitution of identicals.
The Hooded Man
I know that my father is a kind man. I see a hooded stranger and do not know him. If someone argues, 'The hooded man is your father, and you know that your father is kind, therefore you know that the hooded man is kind,' this is fallacious. The intensional context ('know') blocks substitution.
A MOMENT TO REFLECT
Put it to work.
Can you identify a situation in daily life where you or someone else substituted identicals in a belief context, leading to a mistaken conclusion?
Why is it important to distinguish between extensional and intensional contexts when reasoning about knowledge or belief?
How might this fallacy appear in legal reasoning or eyewitness testimony?
Often confused with
CONTINUE THE CONVERSATION
Source texts
- Logically Fallacious - The Ultimate Collection of Over 300 Logical Fallacies