But when to use thee/thou and when to use you? If you ever took Spanish in school, thee/thou are when you use tu in Spanish, and you is when you use usted. (We think thee/thou is *more* formal, because it's used for the relationship with God in the King James bible, but back when that was written, the assumption was that there was no relationship closer or more personal, so of course that's what you'd use for it.)