I came across this sentence in a grammar book (Japanese Postpositions: Theory and Practice by Noriko Katsuki-Pestemer):
生きんが為に働く。
In order to live, I work.
It is then briefly explained that "ん is an auxiliary verb in the volitional function".
However, I've already seen this kind of structure (masu stem followed by ん) come up in fiction quite a few times without really knowing what it means. Since I could not find any other grammar references on it, I'd like to ask if anyone could explain some more general grammar rules or web links to elucidate this "ん is an auxiliary verb".
Does seeing ん after masu stem always imply it being used this way, with volition?