Larry Trask seems to be violating rules about commas as mentioned in his own guide
I was reading Larry Trask's guide on how to use the comma. His node11.html mentions that we should not use a joining comma before any word other than and, or, but, while and yet.
But in node13.html, he seems to be making some dubious uses of comma violating the rules he has mentioned in his guide. For example,
"So, the bracketing commas shouldn't be there."
The comma used in that sentence is not a listing comma. It is not followed by and, or, but, while or yet. It is not a gapping comma either, and doesn't seem like a bracketing comma. Then why is the comma there?
Trask suggests that we fix such punctuation using semicolons. A comma should precede only the five connecting words he has mentioned: and, or, but, while and yet. For anything else, we should use a semicolon. But he doesn't do so in the next example. Why not?
"This is a good sentence, so you have now got the bracketing commas in the right places."
Solution 1:
"So, the bracketing commas shouldn't be there."
The rule that he cites is about joining commas, which are used between two sentences. The full rule he writes is that:
The joining comma is only slightly different from the listing comma. It is used to join two complete sentences into a single sentence, and it must be followed by a suitable connecting word. The connecting words which can be used in this way are and, or, but, while and yet.
In the first example, there aren't two complete sentences, so he's not violating any rule. It would be a violation if he had written, for example "I ate lunch, the bracketing commas shouldn't be there".
"This is a good sentence, so you have now got the bracketing commas in the right places."
You're conflating the rules again by assuming this is wrong. A joining comma should only precede the words you mentioned. But this is a bracketing comma--note that you couldn't really say "so you have now got the bracketing commas in the right place" without ruffling a few grammatical feathers. Take a similar example:
In many cases a weak interruption does not absolutely require bracketing commas. Thus either of the following is fine:
Shortly before the war, he was living in Paris.
Shortly before the war he was living in Paris.
Both, he says, are correct. The sentence you cite has a weak interruption but it is still a valid use of a comma.
Solution 2:
Unfortunately, he’s dead, so we can’t ask him. I’d venture to say, however, that in each of the sentences you quote, the comma is a bracketing comma, used, as he writes, ‘to mark off a weak interruption of the sentence — that is, an interruption which does not disturb the smooth flow of the sentence.’ He later he says ‘the weak interruption set off by bracketing commas could, in principle, be removed from the sentence, and the result would still be a complete sentence that made good sense.’ That would also seem to be the case with the sentences you quote. They, it is true, don’t have pairs of commas, but that’s because, as he says, ‘If the interruption comes at the beginning or the end of the sentence, use only one bracketing comma.’