Do commas,が(the “but” が) and のだ/のです don’t follow the overall tense?

Question

I have a better grasp now that tense of the entire sentence is determined at the end of the sentence and I do know concepts of historical present and relative clause not affecting what the tense of the entire clause is, but I’ve encountered some examples that I’m not quite sure where or not they are a stand alone as a sentence , thereby not knowing of the sentence is a relative sentence or a complete sentence which in turn makes me question the tenses itself.

First one is commas, probably a sentence like this: something something verb/だ, something something verb/だ.

Does the verb that came before the comma considered a sentence itself and the tense is depending on the verb and だ or is it still dependent on the verb/だ that comes at the end of the entire sentence, the clause that’s after the comma. The clause that came before the comma is a complete sentence and can stand on its own and my interpretation at first was that it’s tense shouldn’t be determined by the verb/だ that comes after the comma. But now I’m not so sure now and what’s confusing is the when both verbs/だ are in different tenses.

The second is the “but”が and the construction is quite the same as the first one: something something verbが/だが, something something verb/だ.

Again, does the tense of the first clause have to follow the tense at the end of the sentence. What about けど, it’s also the same but が is just more formal than けど so I might as while ask it. Also でも is definitely out of the picture cause it can only appear at the start of the sentence and not at the “tail” of the sentence so the sentence: something something verb/だ。でもsomething something verb/だ. I feel completely confident that the tense of the clause that comes before でも isn’t affected by the tense after the でも. Just asking for confirmation.

And finally のだ、のです: something something verb/だ, something something verbのだ/なんだ

This is about the the clause that comes after the comma, something something verbのだ/なんだ. If the verb/na adjective is in past tense then is the tense in the past or is it present cause のだ is in present and not のだった. Likewise if the verb/na adjective are in the present, should it be present or past if it is のだった, and also how does it affect the entire sentence as a whole, including the clause before the comma. I’m really confused and would like some help.

Probably this will help with my horrible explanation. Although not having all but most of it is kinda like this. Just what is the tense of both of theses clause?

Answer 1

With clauses linked by から, けど, が the tenses of the two clauses are independent. It would be rather limiting if they were not.

Commas are grammatically uninteresting (see this link).

For でも, as you say, it begins a new sentence so what comes in the previous sentence does not affect the tense of this sentence.

And finally のだ、のです: something something verb/だ, something something verbのだ/なんだ

Really not sure what you mean by this. For future questions it's helpful to provide example sentences. However, adding のだ to the end of a sentence does not require you to change any tense in the previous clause(s). Roughly speaking Xのだ means "It is the case that X". Q: "Why were you sick?" A: "食べすぎたんだ / It's that I over-ate". Q: "Why do you have indigestion tablets?" A: "食べすぎるつもりなんだ¹ / It's that I intend to overeat". I'd claim that the first example is past tense and the second example is future tense, but adding んだ does not change that.

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_{1. I hope that's a natural sentence. Apparently nobody in the history of the internet ever uttered it, according to Google.}