Take a moment to consider this question: “Aren’t I meeting your parents tomorrow night?”

We certainly would never say “are I not?” We would say “am I not?” It seems to follow, then, that we should say “amn’t I?” as a contraction. Why do we not? The answer appears to be simple: because it sounds bad. A word with two consecutive nasal consonants does not exactly roll off the tongue. Remember, languages evolve organically to suit their speakers.

“Ain’t” seems like a compromise between the two camps and is used by a great number of English speakers (principally North American) today. Curiously, the largely forgotten “amn’t” still has sticklers among the Irish. Yet “aren’t” is the most universally accepted contraction, grammatically peculiar though it may be.