Is this が at the end of the verb conditional ?


[![enter image description
here](https://i.stack.imgur.com/mvwdn.jpg)](https://i.stack.imgur.com/mvwdn.jpg)

> だが[殺]{ころ}した **が** [最後]{さいご}きさまあの[世]{よ}いきだ！

I understand this sentence as, _'if you kill him, you are following him to the
netherworld'_.

I intuitively understand this が as conditional but I am not sure. I haven't
found anything which ascertains or confirms this. But I have a strong feeling
of it being a conditional. What kind of が is this and what is it called ?
Also, is this some kind of polite form of たら・なら・ば ?

I've tried searching for this but I think I am missing its name or I am not
searching it right. Any links relating to this would be awesome.

Thank you!




Your basic understanding of the sentence is correct. It means "Once/If you ～,
(something very bad will certainly follow)."

It should be memorized as a fixed pattern, but grammatically, this 殺した is
working as a noun, and が is a plain subject marker. So it can be read as
"Having killed (my son) is (your) end" or "Killing is the point of no return."

In archaic Japanese, attributive form (連体形) of a verb was used instead of の/こと
to nominalize a verb. You may see similar grammar in well-known traditional
proverbs like
[逃げるが勝ち](http://jisho.org/word/%E9%80%83%E3%81%92%E3%82%8B%E3%81%8C%E5%8B%9D%E3%81%A1),
[聞くは一時の恥](http://jisho.org/word/%E8%81%9E%E3%81%8F%E3%81%AF%E4%B8%80%E6%99%82%E3%81%AE%E6%81%A5%E8%81%9E%E3%81%8B%E3%81%AC%E3%81%AF%E6%9C%AB%E4%BB%A3%E3%81%AE%E6%81%A5)
and
[袖振り合うも他生の縁](http://jisho.org/word/%E8%A2%96%E6%8C%AF%E3%82%8A%E5%90%88%E3%81%86%E3%82%82%E4%BB%96%E7%94%9F%E3%81%AE%E7%B8%81).
Basically ～が最後 is [one of the fixed phrases using archaic
grammar](https://japanese.stackexchange.com/a/42724/5010).




> 「Verb in Past Tense + **が** or **ら** + 最後{さいご} + Phrase」

should be remembered as a set phrase meaning

> "Once/If A happens, B will also surely happen."

Thus, the line

「殺{ころ}した **が** 最後、きさまあの世{よ}いきだ！」 means:

" **If you kill him, you will surely go to Heaven (as well)!** " (literal TL)

or

" **If you kill him, I will kill you, too!** " (free TL)

