One of the funniest things about English is the fact that it has the same word for the second person singular and for the second person plural. If I say "I'm going now, and I'll see you later." "You" can refer to one person, to two people, to ten people, or to a crowd of three hundred people. It's still "I'm going now, and I'll see you later."
That's not the case in some other languages. In German, for example, I'll use "du" if I'm speaking to one person, but "Sie" if I'm speaking to two or more people. "Du" is the second person singular, and "Sie" is the second person plural. (If you want to be painfully polite, you'll use the second person plural to speak to someone you really want to impress, but that practice is dying out.)
In English, however, "you" does double duty as both the second person singular and the second person plural.
It wasn't always like this. "You" was once only the second person plural in the English language. Back in the day when Shakespeare wrote his plays, when Cranmer compiled the Book of Common Prayer, and James I (James VI if you're Scottish) commissioned his scholars to produce a new translation of Scripture, the second person singular in the English language was "thou / thee / thy". People tended to use "you" as a second person singular at times when they wanted to be very polite (with a similar feel as the "royal 'we'"), and eventually the use of "thou / thee / thy" tended to die out in most normal speech.
Today, "thou / thee / thy" is seen as specialised religious language (and, for that matter, "thou / thee / thy" is rarely used in the churches). "Thou / thee / thy" is most often used in comedy routines in which members of the clergy are lampooned. Functionally, "you" is both the second person singular and the second person plural.
Except ... in some geographical areas, there are other words used as a regional second person plural.
- In the southern United States, "y'all" is used as a second person plural. If you're bidding farewell to two or more people, you may say "I'll see y'all later."
- In western Pennsylvania, "yunz" (or "yinz") is used in a similar way: "I'll see yunz later."
Here in Australia, there are some people who have developed "youse" as the second person plural (as if they were characters in a B-grade gangster movie from the '40s). "Youse" tends to be more socially specific than "y'all" or "yinz". To say "I'll see youse later" normally marks a person of a working-class background, of minimal educational attainments, and more frequently male than female. (Either that, or the person saying "youse" is trying to be funny.)
The existence of "yunz", "youse", and particularly "y'all" points to a need that exists within English.
Like speakers of other languages, speakers of English occasionally need a second person plural that is distinct from the second person singular. For example, when taking leave of a group of people, all of whom you'll see on the weekend, but one of whom you'll see before that, which statement works better?:
- "I'll see you on Saturday, but I'll see you on Thursday."?
- "I'll see you on Saturday, but I'll see thee on Thursday."?
- "I'll see y'all on Saturday, but I'll see you on Thursday."?