Let's look at some examples:
— Would you like some ice cream?
— Are you happy?
According to Wiktionary “yes” is a particle:
Used to show agreement or acceptance...
“No” and “Yes” are sentences, they start with a capital letter and end with a period.
However, a particle cannot be either a subject or a predicate. Thus, we have the sentences without a subject and a predicate. What is weird.
So, I want to understand, what parts of speech and sentence constituents are "yes" and "no" in such cases.
According to etymonline.com:
Old English gise, gese "so be it!," probably from gea, ge "so" (see yea) + si "be it!," from Proto-Germanic *sijai-, from PIE *si-, optative stem of root *es- "to be."...
It turns out, that "yes" etymologically means "so to be".
Could it be that "yes" and "no" are not particles, but something like verbs which express being or nonbeing of agreement? Could it be that in this way they are actually predicates, and subjects are the essences of questions, which are not repeated in the answers but are implied?