I am aware that classical Latin did not have words for "yes" and "no" in the same sense that English does. I know that they could express the idea of "yes" by either using the verb of the question that was asked in the affirmative sense, or by saying something like "ita" or "sic".
My question here is more related to the evolution of the word "sì" in the Italian peninsula. Of course the modern Italian word "sì" comes from the Latin "sic". Additionally, the Italian word "così" (which means "like so" or "like this" or "thus") also comes from the Latin word "sic".
Based on documented evidence through historical texts, do we know when people living on the Italian peninsula began to use the word "sì" to mean "yes" in their typical everyday speech? Is there any evidence that they were already saying "sì" even during the classical Roman era, even if it was informal and wasn't used in formal Latin writing styles?
We know that "sì" was already in common use by the time of Dante, as he called Italy the "bel paese là dove 'l sì suona" (the beautiful country where "sì" is heard). But that means it must have come in to common use well before his time. I'd like to nail down exactly when "sì" became the common way to say "yes" in typical speech on the Italian peninsula. Any ideas? Thanks!