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Masked man fallacy

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Cogito ergo sum
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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 indiscerniblesWikipedia) is used improperly.

The masked man fallacy is a formal fallacy.

Alternate names[edit]

  • Epistemic fallacy
  • Hooded man
  • Illicit substitution (of identicals)
  • Intensional fallacy


Alice: "Do you know this masked man?"
Bob: "No. "
Alice: "But he is your father! Hey folks, Bob doesn't know his own father!"

This is also an example of information asymmetry as Alice knows something Bob doesn't.

P1: I know who Ann is.
P2: I do not know who the masked man is.
C: The masked man is not Ann.


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"

External links[edit]