Difference among んがため and べく?


could somebody help me understanding the difference between んがため and べく? They
both mean "In order to", but I don't think they are interchangeable. Could
somebody provide me some examples to understand the difference?




べく is stiff and literary. んがため is even more literary and often theatrical.
This ん is an archaic volitional auxiliary, and が is an archaic possessive
particle explained [here](https://japanese.stackexchange.com/q/39264/5010).
Grammatically (ん)がため works like のため. See also: [Is there a difference between
んがため and ために?](https://japanese.stackexchange.com/q/5396/5010)

