y'all

It's a contraction, short for "you all" -- a distinct second-person plural for a language that doesn't have one.

Let's do the math:

you + all = youall; substitute ' for the ou = y'all

It's not ya'll.

*If* there existed a contraction for the phrase "ya will" (if there existed such a phrase), *then* that contraction might indeed be ya'll (ya + will = yawill; substitute ' for wi = ya'll).

But the thing is, people don't say ya will, so there is no contraction for it, so IT'S NOT YA'LL!

It's Y'ALL!

I realize no one but me cares about this. I don't even know why I care about this -- overcaffeination, perhaps? -- but I do. Deeply.