ah so

[Natalie Maynor]

> Natalie asks about the origin of "ah so". In Japanese, "Ah, so desu ka?"
> (the "u" is voiceless or elided) is a very common backchannel response, ~~
> "Oh, is that so?"

I wasn't asking about its origin.  I've heard "ah so desu ka" and other
"ah so" expressions, including "ah so" by itself, many times in Japan.
What my friend was trying to figure out is why that particular expression
was latched upon by speakers in the US at some point.  I would guess
that most US speakers are familiar with it and not from having spent
time around Japanese speakers.
   --Natalie Maynor (maynor at ra.msstate.edu)