Is this が at the end of the verb conditional ?

Question

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!

Answer 1

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, 聞くは一時の恥 and 袖振り合うも他生の縁. Basically ～が最後 is one of the fixed phrases using archaic grammar.

Answer 2

「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)

Answer 3

This ~が最後 is a special use of 最後, which has the same meaning as ~たら最後.

This dictionary entry describes it as follows:

２ （「…たら最後」「…が最後」の形で）それで終わりで、あとはどうにもならない意を表す。一度…したら、それっきり。「走りだしたら最後、止まらない」「食いついたが最後、離れない」

It means that there is nothing that can be done about X, if Y has happened.

Basically, this can be translated as "As soon as X, Y". Thus, your sentence can be translated as: "However, as soon as I kill you, you will be going to the other world!"

So, it is not a mistake, it is just another version of ~たら最後.