Consider the following two examples:

At the turn of the century, the form ain't was prestigious among many upper middle class English speakers in southern England. Today, however, its use is considered non-standard or at best appropriate only for casual conversation.

In the United States "dropped r's" in words like car, father, and bark are perceived as features of nonstandard speech. In Britain, however, "dropped r's" are characteristic of upper class pronunciation and are thus considered part of the prestige dialect.

What do these two examples tell us about standard and nonstandard features? Are they defined on linguistic or social grounds? Explain your answer.