Jack Chambers, University of Toronto linguist, writes that these “ehs” are all of a piece. “All of these uses have one pragmatic purpose in common: they all show politeness,” he wrote in a 2014 paper. Using “eh” to end the statement of an opinion or an explanation is a way for the speaker to express solidarity with the listener. It’s not exactly asking for reassurance or confirmation, but it’s not far off: the speaker is basically saying, hey, we’re on the same page here, we agree on this. Even in the use of “eh” as a criticism or a command, the word seeks to find common ground. If I say “you’re an idiot, eh?”, what I’m saying is, you’re an idiot, but you should also think you’re an idiot, and our understanding of you as an idiot finds us on common ground.