This is unusual because one is more likely to be not a witch than be one as no one knows what makes a witch for certain.
Explanation:
In Act 3 of the play Martha Corey must tell the court and convince them that the allegation against her for being a witch is false.
She does this by giving her logic the way she can but is asked this bizarre question “How do you know, then, that you are not a witch?”.
The fault in the question is that by probability one cannot know someone to be a witch by guess because witches do not exist or as they believed in their time were rare.
So, for a woman to be declared one, the court would need definite proof for it to be true.
