In Old English, thou/thee were used to address a single person, while ye/you were used to address more than one person. However, as English developed, the terms ye and you were used to politely address a single person – first the king, then other high born nobility and the clergy, and eventually anyone at or above a person’s social status.
By the end of the 16th century, the word ye had virtually disappeared from daily speech, and the term you was quickly replacing the term thou.
As Early Modern English began, the word thou became associated with emotions, rather than number or hierarchy, and most people would only use thou if they were angry or in love. Ironically, these days people very rarely use the informal thou to indicate formality or to sound more archaic: “Thou shallt not lie.”
