Here's a breakdown of what we know:
* Old English: The closest ancestor of "yes" in Old English was "gea" or "ge" meaning "ever," "always," or "always so." This was a common affirmative response.
* Middle English: Around the 12th century, the word "yes" started appearing in texts, probably derived from "gea." It wasn't universally used, and variations like "ya" or "ye" were also common.
* Modern English: By the 16th century, "yes" became the standard affirmative response in English, replacing other variations.
It's crucial to understand that language evolution is gradual. There wasn't a specific day "yes" suddenly became a word. It emerged through subtle changes in pronunciation, spelling, and usage over a significant period.
Therefore, while we can't give an exact date, we can say "yes" developed from Old English forms like "gea" and became the dominant affirmative response in English by the 16th century.