When a speaker of Standard American English (SAE) suddenly resorts in an otherwise completely standard utterance to an obvious colloquialism, “ain’t” for “isn’t,” as did a professor being interviewed on NPR this morning (“Morning Edition”), one wonders what the function of this stylistic shift might be. The only answer that makes sense is EMPHASIS. Since the word “ain’t” is a negation, other than resorting to suprasegmental means (loudness, intonation), the speaker has only this stylistic item at his disposal in order to call heightened attention ––i. e., to a higher degree than communicated by the neutral SAE negation “isn’t”––to the fact that the meaning intended involves emphasis.