I'm finding conflicting guidelines about the use of commas with subordinate clauses. What are the rules?
Also, which of the following is correct, and why?
- Some of what Mike did needs to be adjusted.
- Some of what Mike did, needs to be adjusted.
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Comma usage in English language is a difficult problem to resolve. There are rules, there are rules against those rules and there are recommendations.
In situations like these, the best you can do is use your common sense and ask yourself: does a comma here helps the reader understand the sentence?
In your sentence it's definitely not required, but I'd say it's "legally optional", as it tells the reader which part of the sentence the "did" belongs to. Not that it's ambiguous, but it could possibly belong to the second part of the sentence. If your brain reads too fast, it could interpret it as:
I know, I know, I'm exaggerating here, but you get the point.
The problem arises when you put the comma where it absolutely cannot be. From the history of the questions on this site, I expect that sometimes in 2013 a user will post the following sentence:
Again, I'm exaggerating here, but again, you get the point.
TL;DR: Put a comma wherever it helps the reader parse the sentence. Never put a comma anywhere blindly just because it audibly fits.