masked man fallacy

noun1

1. •
   A fallacy of inferring that since one knows (or does not know) something by one description, one must know (or not know) it by another, as in "I know who my father is. I do not know who the masked man is. Therefore, my father is not the masked man."

   • Consider the Masked Man fallacy, which shows that I can know something under one description but not under another. — 1999