Masked-man fallacy
Leibniz's law states that if A and B are the same object, then A and B are indiscernible (that is, they have all the same properties).The fallacy is "epistemic" because it posits an immediate identity between a subject's knowledge of an object with the object itself, failing to recognize that Leibniz's Law is not capable of accounting for intensional contexts.The name of the fallacy comes from the example: The premises may be true and the conclusion false if Claus is the masked man and the speaker does not know that.Another example: Expressed in doxastic logic, the above syllogism is: The above reasoning is inconsistent (not truth-preserving).The valid and invalid inferences can be compared when looking at the invalid formal inference: Intension (with an 's') is the connotation of a word or phrase—in contrast with its extension, the things to which it applies.Intensional sentences are often intentional (with a 't'), that is they involve a relation, unique to the mental, that is directed from concepts, sensations, etc., toward objects.