No, definitely not. In very many cases it would not even be optional. It would simply be wrong.
no. if but before is a sentence on its on and after but is a sentence on its own then put a comma before but.
befor
after
Before. ex. I had every intention of going to the store, but I forgot.
Punctuation is dictated by the meaning of your sentence, not by the presence of particular words. A comma indicates a brief pause. Say your sentence aloud, and where you find that you naturally pause briefly, you will probably find that a comma is appropriate. Other people may punctuate the same sentence differently. That is not necessarily wrong. A lot depends on the context: whether it is formal, informal, written, spoken, and so on. Here are some examples: 'There was nobody in the house but my mother.' (No comma) 'I like cheese, but my sister can't stand it.' (Comma before 'but') 'I would prefer you to stay at home but, if you do go out, please wear a warm coat.' (Comma after 'but') 'I would prefer you to stay at home, but if you do go out, please wear a warm coat.' (Comma before 'but') (The last two examples convey slightly different shades of meaning.) It's perfectly possible to have a comma both before and after the word 'but' if you think the sense requires it, but you should be wary of having too many commas in one sentence.
Yes
No, a comma before "as appropriate" is not necessary. It depends on the context of the sentence and whether it flows better with or without the comma.
No, a comma does not always come before "for instance." It depends on the structure of the sentence. A comma is typically used before "for instance" when it introduces a non-essential or parenthetical element in the sentence.
No. There is no word in English that always requires a comma before it.
Sometimes, but not always. There is no one single rule that applies to "but." ----
Not at the beginning of a sentence. As you know is a clausal sentence adverbial, and as such it should generally be set off by punctuation. That would mean a comma after it at the beginning of a sentence, a comma in front of it at the end of a sentence and commas on both ends when it appears in the middle of a sentence: "He is, as you know, rather obstinate."
No
It depends on the type of sentence. So your answer would be not all the time. I hope that helps! :)
A period should come before the footnote at the end of a sentence, while a comma should not.
,Always.
As always, I enjoyed my time with the kids.
When which is used to introduce a nonrestrictive adjectivial clause it must it must follow a comma. But there are numerous examples where which does not need to follow a comma. Including: Which melon do you want? I can't tell which melon to buy.