Masked Man Fallacy
I know who Bruce Wayne is.
I do not know who Batman is.
Therefore, Bruce Wayne is not Batman.
In the masked man fallacy, a substitution of identical designators in a true statement can lead to a false one. The statement "I do not know who Batman is" gets treated as if it excludes Bruce Wayne simply because I do know who he is. Of course, as long as I don’t know that Bruce is actually Batman, both statements can be absolutely true, and yet the conclusion does not follow logically.
The general form of the argument is:
X is known.A similar argument, however, is valid.
Y is unknown.
Therefore, X is not Y.
Clark Kent is Superman (X is Z).
Batman is not Superman (Y is not Z).
Therefore, Clark Kent is not Batman (therefore, X is not Y).
That’s because being something is different from knowing something. Lack of proof of one proposition doesn’t serve as proof of the counter proposition.