What does a "si" clause followed by a "nisi" clause mean?

Question

In the Vulgate Bible, I came across this sentence.

Vivit Dominus Deus Israel, in cuius conspectu sto, si erit annis his ros et pluvia, nisi iuxta oris mei verba.

[As] the Lord God of Israel lives, in whose sight I stand, there will not be dew and rain these years, unless according to the words of my mouth.

1 Kings 17:1

The translation makes sense, but I don't understand the si...nisi construction. I know the basics of conditionals, but I haven't seen these two words used in combination before. Could anyone explain? Also, where do we get the "not" adverb in the clause, "there will not be dew and rain"?

Answer 1

I found this in an online version of Plater & White's A grammar of the Vulgate:

In emphatic speech, especially in adjurations, si = a negative

Here are some of the attestations:

'semel iuraui in sancto meo, si Dauid mentiar' (=I will not lie unto David) Ps. 89. 34 (88. 36), 'si introibunt in requiem meam' (= they shall not enter into my rest)

If this is true, the function of the Vivit Dominus Deus Israel is to frame the speech as an oath. That's what the translation is trying to convey by adding an 'As' at the beginning.

The Plater and White entry goes on to give an explanation for this behavior:

This si is not really a negative. The 'not' comes from a suppressed clause, 'if... (then my oath will be in vain', which in the case of God it cannot be).

Answer 2

It doesn't make any sense because it's not a Latin construction. The Latin appears to be a translation of the Greek:

εἰ ἔσται τὰ ἔτη ταῦτα δρόσος καὶ ὑετὸς ὅτι εἰ μὴ διὰ στόματος λόγου μου.

This is in turn is a rather literal "translation" of the Hebrew:

אִם־יִהְיֶה הַשָּׁנִים הָאֵלֶּה טַל וּמָטָר כִּי אִם־לְפִי דְבָרִי

You'll notice the parallel construction: εἰ...εἰ μὴ || אִם...אִם

In Hebrew, אִם is a conjunction that covers a range of meanings, and of course it (and Hebrew in general) doesn't work the same as Latin, Greek, or English.

Answer 3

This is conditional sentence, and 'si' is the sign of the conditional here; 'Si', (if) with 'nisi' (unless) , the negative ni- refers to the principal clause, which is thus denied, if the conditional clause is accepted; (Gildersleeve & Lodge) There is also said, the negative of 'si' is 'si non' or 'nisi'.

Mind there are no similar examples given so it must be as C. M. Weimer said, 'not a Latin construction'.