ざるをえない vs しかない

[katafei]

行きたくないけれど、部長の命令だから、行かざるをえない。
I don't want to go, but it's my bosses orders, so I'll have to go.
試験を受けるからには、頑張るしかない。
Since I'm taking the test, I'll have to do my best.

I was wondering if there is a significant difference in the meaning of ~ざるをえない and しかない. I know the first is a little archaic, but other than that, they seem pretty much interchangeable to me. Am I right here?
Any pearls of wisdom are more than welcome ^_^

[Yudan Taiteki]

行きたくないけれど、部長の命令だから、行かざるをえない。
I don't want to go, but it's my bosses orders, so I'll have to go.
試験を受けるからには、頑張るしかない。
Since I'm taking the test, I'll have to do my best.

I was wondering if there is a significant difference in the meaning of ~ざるをえない and しかない. I know the first is a little archaic, but other than that, they seem pretty much interchangeable to me. Am I right here?
Any pearls of wisdom are more than welcome ^_^

To me, ざるをえない means that you are required to do something, whereas しかない marks the best alternative among a number of bad ones. But ざるをえない is kind of formal or written so I don't have a good handle on when it's appropriate to use.

[richvh]

I think ざるを得ない is closer to しかできない than it is to しかしない, the first two being "can't do anything but..." where the latter is "won't do anything but..."

[spin13]

行きたくないけれど、部長の命令だから、行かざるをえない。
I don't want to go, but it's my bosses orders, so I'll have to go.

To me, ざるをえない means that you are required to do something,

Not just being required to do something, but required to do something you don't want to do. The example explicitly includes a desire to not go, but the feeling would be about the same even without it. I would compare it to the English phrase "can't get out of it".

～しかない can be much more mundane. For example:
A: "キリンを下さい。"
B: "ごめんね、アサヒしかない。"

There is no requirement to drink the Asahi but there just simply isn't any Kirin. The disappointment goes only as far as not being able to drink Kirin, which, honestly, isn't that big of a disappointment at all. You'd have to be a Kirin employee with one hell of a boss to get as far as, "キリンを飲まざるを得ない".

-Eric

[Bucko]

ざるをえない is mainly for written Japanese. It might be useful to note that there is another form which means the same: わけに（は）いかない. わけに（は）いかない can be used in both no-choice and obligation situations, and implies the speaker's unwillingness to do something indicated by the verb, whereas both ざるをえない and しかない are used in a no-choice situation.

[katafei]

Thanks people, i think I understand it a bit better now!

And I'm dying to try a キリン ^_^