Dialects are little subsets of a language, and they have their own vocabulary, syntax, phonology, and grammar that sometimes overlap with other dialects of the main language and sometimes don’t. “Y’all” is a dialectal term for the second-person plural pronoun; it’s completely standard in some dialects of American English, particularly the ones in the South, and while it’s common to hear speakers of those dialects use it easily, it’s not a normal part of the dialect we call Standard English. We tend to think of dialects (insofar as we think of them at all) as regional—Southern English, Boston
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