Examples of comma rules

Question

I am refreshing - or rather building up from scratch =) - my knowledge about the proper usage of commas in the English language. I would like if you could take a look at the subsequent examples and check if they are correct.

1. Due to/Since/Because ...., we can...

   A comma because the first clause is an adverbial "clause of reason". If the dependent clause would stay behind the main clause, then there would be no need for a comma.

2. A converges to B, locally uniformly.

   Here, I am not sure. It looks better with a comma for me, but I believe, there is no need for a comma since the second clause is essential ?

3. We saw the key which we will need later on the roof.

   Here, I am not sure. Does the comma-usage here just depends on the essentiality of the clause introduced by which? The car which had the most people in it weights the most. -> essential clause The car, which looked very nice, weights 1200 Kg.-> non-essential clause

4. "Thus/Therefore/Hence" at the beginning of a sentence: Comma right after the word? I think, no.

5. It states that if ..., then ....

Answer 1

1. Correct. If the dependent clause concludes the sentence, no comma is necessary. Example: "We can drive to the island because the bridge is open."

2. Your example sentence is not clear enough for me to understand what you are asking, but I think you are giving an example in which a comma is preferred.

3. Yes. Whether the clause is essential or not determines the need for the comma. Essential, however, is not the usual grammatical term. Restrictive is the term you are looking for. If the clause is restrictive (essential), then you do not use commas.

4. This one is not hard and fast. A comma tends to be used, but not always.

5. This one is also somewhat a matter of preference.

Comma rules are complicated, numerous, and debatable, and sometimes come down to a matter of stylistic preference of the author. Most of us who want to learn about commas tend to refer to the work of a teacher named Larry Trask, who put a rather long work about commas online at this URL:

http://www.sussex.ac.uk/informatics/punctuation/

Go there, and be enlightened. :)

Answer 2

Two rules for commas. Even three:

No comma if a conjunction is inside, not at the beginning:

• Call me [no comma] if you are free.
  but:
• If you are ill, you ought to see a doctor.

No comma before a clause which provides no extra information:

• This is the man [no comma] I saw yesterday.
  but:
• I went to the London Palladium, which a friend of mine recommended.

No comma after please at the beginning:

• Please come in.
  but:
• Come in, please.

Comma rules have many issues and I came across a large PDF to study. It's not that easy to answer.