Maybe we should approach a mixed group of people and say, "How are all you gals?"

Okay, I'm entering the discussion...y'all.

Standard English recognizes only one second-person personal pronoun: you. In modern usage, this pronoun is used for both the second person singular and second person plural.

Most languages have at least two personal pronouns for the second person. In many cases, there are three, as in German:

Second person singular (informal): du
Second person singular (formal): Sie
Second person plural: ihr

Early English was heavily influenced by Germanic pronoun forms. By Shakespeare's time these had normalized as:

Second person singular (informal): thou
Second person singular (formal) or second person plural: you

Thou retained its Germanic declensions: thee (object) and thy (possessive). Thou also required Germanic verb conjugation (thou hast--compare to the German du hast). Ease of use (lack of both declension and conjugation) may be part of the reason that you became more commonly used [my conjecture only]. But for whatever reason, thou eventually fell out of favor, leaving only you to carry the weight for the second person singular and plural.

Note that we have lost the formal you (Sie-form) altogether. I say good riddance to it--English has become a more egalitarian tongue without the forced formality that plagues so many languages.

Naturally, having only one pronoun for both singular and plural often creates confusion because it is not always clear whether you refers to only one person or to more than one. Many attempts have been made to clarify the situation. In the Southern US, we have settled on the convention of y'all. Personally I find this far more elegant than any of the other American attempts at synthesizing a second-person plural personal pronoun (e.g. y'uns, youse guys, etc.). With all respect to my Northern neighbors, these all sound coarse to my ears.

I contend that y'all very neatly takes the place of of the old plural you, freeing up the modern you to concentrate on its role as the modern version of the singular thou.

Please note: y'all is always plural. Always, always, always. You will occasionally hear people insist otherwise, but that is simply not how it's used. Those who say otherwise are yankee interlopers.

There is, however, another "super-plural" form: all y'all. This is used when addressing multiple groups or when emphasizing the totality of a very large group.

Example: I need y'all (Group A) over here and y'all (Group B) over there, and at the end I want all y'all (Groups A & B) to come down here.

I hope I didn't bore y'all too much with this. To my fellow Texans and other Southerners, I know y'all get it. I just wanted all y'all to understand the proper use of this invaluable word.