correct spelling: y'all
Southern 2nd person plural pronoun. Most concise and easily distinguished. Despite the assurance of some emails that have been passing around, "y'all" is plural. Only an absolute idiot would use it as a singular pronoun.
Where are y'all going?
contraction for you all. Despite what some think, it is not only used by hicks and the uneducated. People from all walks of life, traditionally the southern states use it.
Hey y'all, McJ is an idiot
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Y’all clearly arose as a contraction of you-all. Y’all fills in the gap created by the absence of a separate second person plural pronoun in standard modern English. This absence arose when thou/thee (singular) and ye (plural) disappeared, and you came to signify both singular and plural. This absence similarly gave rise to the phrases you-uns, you lot, or you guys. (Cf. yous, an informal plural second-person pronoun formerly used in New York City, still common in Ireland, often rendered "youse" in Australia and New Zealand, and yinz, an informal plural second-person pronoun commonly used in Western Pennsylvania and the Appalachians).
Though the you all contraction argument may make sense when considering current-day vernacular, it is prudent to consider the vernacular which existed at the time which y’all was likely invented. By the late 18th century, Scots-Irish immigrants had settled in the Southern United States. It is well established that Scots-Irish immigrants frequently used the term
ye aw. Some evidence suggests that y’all could have evolved from ye aw due to the influence of African slaves who may have adapted the Scots-Irish term.