Where does the いかない in ～わけにはいかない come from?


My first thought is that いかない in this phrase conveys the meaning of 行かない, that
is, not progressing to something. But this is mere guesswork.

What is the history of いかない in ~わけにはいかない? Does it have roots in the verb 行く or
is this way off base?




From what I gathered from reading [Steven Pinker's _The Stuff of
Thought_](http://en.wikipedia.org/wiki/The_Stuff_of_Thought), humans evolved
in a world with tangible physical objects and obvious physical actions, so
almost all of our thinking is based in that reality.

As a result, most of what appears to be highly abstract thinking is actually
built on our attempts to attach metaphors of tangible things and actions to
intangible concepts.

Which is an academic way of getting around to the fact that I think you'll
find the concept of "go", or `行く【い・く】`, to most likely come to take on a
meaning of "possibility" in a lot, if not all, languages.

In a tangible world, a ball can not go to another place if there is a wall
between here and there. And so it follows that the abstract ball can not
achieve its destination if a conceptual barrier prevents it. Resulting in an
attachment of an idea can not become possible because it can not "go" there.

I believe what you are looking for, then is an origin of how `行く` came to take
on the meaning of "possible" in a Japanese context, but I think the reality is
that it is more of a broader issue, and so you are unlikely to find an
etymological explanation that is exclusive to Japanese.

The one thing I think can be said that is strictly defined in the realm of
Japanese is that it is more common to see `行く` written in kana, `いく`, when
used in the more metaphorical sense, as in the phrase `訳にはいかない`. Not a hard
and fast rule by any means, but I believe that to be the case, because the
kanji is tied too much to the literal "go".

Also, just as sort of "bonus reading", see [this
page](http://okwave.jp/qa/q903786.html) for a bit of discussion in Japanese
about how exactly `訳にはいかない` is used. I hadn't really thought of it in
opposition to `したい`, as one answer puts it.

