(Epicurus - On Nature - Book 28, P.Herc. 1479 (1417), fr. 13, col. 9 sup., David Sedley trans.)
"...these will be confuted, if they are false and whether the cause of their error is irrational or rational, either because (1) some other than theoretical opinion expressed on the basis of them is untrue, or, (2) if they become indirectly linked up with action, wherever they lead to disadvantageous action. If none of these consequences ensues, it will be correct to conclude that opinions are not false. For this reason, everybody can easily laugh when somebody gets another to assert that it is impossible to know and not know the same thing, and then cites the riddle of the Covered Father, and others of the same kind."
What is the “Covered Father Riddle”? Also known as “the Megarian Riddle”?
It's often used as an example of a paradoxical situation in philosophical discussions about knowledge and truth. The riddle attempts to force one to admit they both know and do not know something.
This riddle presents a scenario where a father is covered with a blanket and his son is asked to admit that he does not know who is beneath the covering.
The paradox arises because if the son says he doesn't know who is under the blanket, it implies that he doesn't know who his father is, which is strange because he should know his own father.
Therefore it is an apparent paradox that the son simultaneously “does not know who” is under the blanket and “does know who” is under the blanket. Really the error is in the language, as the son in fact simultaneously “does not know who is under the blanket” and also knows “who” is under the blanket.
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The riddle, known as the "Riddle of the Covered Father," may come from Diodorus Cronus (Διόδωροc Κρόνοc; died c. 284 BC).
Zeno of Citium was one of his pupils, and Epicurus was probably, in part, responding to him in this book.
Diodorus was also known for these other silly and better known "paradoxes":
The Horns paradox (ὁ Κερατίνηc): What you have not lost, you have. But you have not lost horns. Therefore, you have horns.
The Sorites paradox (ὁ Cωρείτηc): If you have a heap of sand and you remove one grain, it's still a heap. Continuing to remove grains one by one, at what point does it cease to be a heap?
