Difference in sentences using は+が vs は+は

Question

So I've come across these two sentences:

1. 雨は降っていますが、雪は降っていません

and

2. 雨は降っていません。雪が降っています。

so what i think is happening is that the first sentence shows contrast.

in the first sentence, we simply introduce two topics and give information about them.

in the second sentence we introduced one topic, and since we already mentioned 降っている it became old information and then we can use が to specify what does come down/fall.

it's a sentence that doesnt come to contrast but to show correction/specificity of the topic.

is that correct..?

Answer 1

With all due respect, I disagree with your analysis, especially of the second sentence.

First of all, I don’t think the existence of the first part in each sentence is very important. The question seems to have more to do with how to interpret が and は in a negative sentence.

雪が降っています is a very natural, matter-of-fact sentence that states it is snowing. However, its negative version 雪が降っていません sounds as if the state described by 雪が降っています is the normal or expected state, but that state is currently not fulfilled because snow is missing.

雪は降っていません, on the other hand, specifically negates 雪 as something that is falling. Something else might be falling.

Your first sentence sounds natural because of this. 「雨は降っていますが、雪が降っていません」 would imply it is supposed to be snowing, too, and that would sound weird.

Your second sentence could be either 「雨は降っていませんが、雪が降っています」 or 「雨は降っていませんが、雪は降っています」. The latter somewhat emphasizes the fact that snow is coming down from the sky although rain is not.