In Act 3.1 of Shakespeare's Hamlet, in the nunnery scene as you call it, Shakespeare uses a paradox (he uses other devices, as well, but I'll stick to this one: the others are admirably covered above).
Hamlet says in lines 113-115:
Ay, truly, for the power of beauty will sooner tansform honesty from what it is to a bawd than the force of honesty can translate beauty into his likeness. This was sometime a paradox, but now the time gives it proof. I did love you once.
Hamlet says that beauty can turn honesty, or chastity, into a pimp or a whore, more quickly than honesty, or chastity, can change beauty into a virgin. Beauty can turn a woman into a bawd, but honesty or chastity cannot change a beautiful woman into a virgin.
Hamlet is indirectly condemning Ophelia for the role she is playing for Claudius and her father, Polonius--the role of spy. She has been hired, so to speak, to return Hamlet's gifts and pretend she doesn't love him, in order to see how he reacts, and to help determine the cause of his madness.