Masked man fallacy
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A masked man fallacy is a logical fallacy that occurs when one confuses knowing what a thing is with knowing what every single instance of that thing is. It occurs when Leibniz's law (Identity of indiscernibles) is used improperly.
The masked man fallacy is a formal fallacy.
 Alternate names
- Hooded man
- Epistemic fallacy
- Illicit substitution
- Illicit substitution of identicals
- Intensional fallacy
“”Ann: "Do you know this masked man?
This is also an example of information asymmetry as Ann knows something Bob doesn't.
- P1: I know who my friends are.
- P2: I do not know who these masked men are.
- C1: They are not my friends.
It is not always proper to replace one term for another even if the two terms designate the same thing, nor can one automatically assume that subjective knowledge of one person (or even of a group) is necessarily enough for making accurate, non-contradictory statements or for teasing out inherently contradictory definitions.
Another way of looking at this issue is confusion between the quotation and the referent, equivalence in beliefs and equivalence in reality. Two labels may happen to refer to the same thing in the territory, yet be distinct labels on the map, especially if the one holding the belief does not know about their equivalence.
- masked man = father
- "masked man" ≠ "father"
- See the Wikipedia article on Masked man fallacy.
- The Masked Man Fallacy, Fallacy Files
- Intensional, Internet Encyclopedia of Philosophy
- The Quotation is not the Referent, LessWrong