Ｖneg + ざるを得ない : used in a situation where one has no choice but to do something.

Ｖ + しかない : used in a situation where one has no choice but to do something.

What is the difference, if any, in nuance between these two grammar points?

I think http://thejapanesepage.com/forum/viewtop...=7&t=11231 does a pretty good job (not too in depth, but good enough) at differentiating them.

Basically, ざるを得ない is more like, you "can't get out of it," ie. there's something you don't want to do, but you've gotta do it anyway.

しかない is like "there's nothing else to do," so you've gotta do it.
So like, the example I liked was about beer

キリンがないから、アサヒを飲むしかない
(assuming you're going to drink beer anyway), there's no Kirin, so you've gotta drink Asahi
Whereas...I really can't think of a situation where you'd have
アサヒを飲まざるを得ない, unless you work for アサヒ and you'll get fired if you don't drink it...

Aha. Wakatta.

Is しかない more casual/spoken as well? I certainly get that impression, whereas ざるを得ない would be used in a more serious situation / written down?

Cheers Asriel.

Yeah, to be honest I've never heard ざるを得ない in real life, but しかない is really quite common.

"The trains have stopped running so, 歩くしかない"
and stuff. It comes up in conversations quite a bit.

Yep, same here. I've heard しかない a lot, whereas I've only encountered ざるを得ない in Japanese class.

Aah, just realised more confusion. What about:

ない－わけにはいけない
ないーなければならない

しかない is really common. I've heard ざるを得ない come up in doramas a few times. Best recent example is 生き残るためには多少、汚い手を使わざるを得ない。

わけにはいかない is less of a literal obligation, and also goes with things you shouldn't do rather than things you should do.

本彼女がきっといるから、行くわけにはいかない。 = My ex-girlfriend will definitely be there, so there's no way I can go.
頼む人は部長だから、断るわけにはいかない。 = The person asking is the section chief, so I really can't refuse.

(Note that it's いかない not いけない; it's easy to mess up, particularly because of ～てはいけない)