While Modern English has a two-form system of yes and no for affirmatives and negatives, earlier forms of English had a four-form system, comprising the words yea, nay, yes, and no. In essence, yes and no were the responses to a question posed in the negative, whereas yea and nay were the responses to positively framed questions.
Will he not go? — Yes, he will.
Will he not go? — No, he will not.
Will he go? — Yea, he will.
Will he go? — Nay, he will not.
This is exemplified by the following passage from Much Ado about Nothing:
Claudio: Can the world buie such a iewell?
Benedick: Yea, and a case to put it into, but speake you this with a sad brow?
— William Shakespeare, Much Ado about Nothing, Act I, Scene I
Benedick's answer of yea is a correct application of the rule, but as observed by W. A. Wright "Shakespeare does not always observe this rule, and even in the earliest times the usage appears not to have been consistent." Furness gives as an example the following, where Hermia's answer should, in following the rule, have been yes