Ah, yes, the parenthetical comma:
How on earth I we going to clear this up, I wonder, as I reach the living room. |
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versus the comma before a co-ordinating conjunction:
How on earth I we going to clear this up I wonder, as I reach the living room. |
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versus the comma separating off the introductory elements in a sentence:
How on earth I we going to clear this up, I wonder as I reach the living room. |
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They're all entirely correct.
At which point I think you go for the one which suits the rhythm of the sentence - i.e. the voice - best. As David Crystal says, punctuation has two sometimes conflicting jobs: expresses grammatical meaning, and expresses how something is actually said.
It's one of the fights I've had with US copy-editors in particular: they always seem to want to turn everything to parenthetical commas, and often that's not appropriate, especially in anything as voice-y as fiction...
<Added>I can feel a blog post coming on. It's a while since I've done anything that technical
<Added>Super-technically, I'm not sure "as" is a co-ordinating conjunction. But there are limits to even my punctuation-nerdiness...
<Added>ERRATUM
in the examples,
for "I" read "are"...