Grammatically Correct: The writer's essential guide to punctuation ...

GRAMMATICALLY CORRECT
is about to leave (whether on her own or with someone else), and
just then Jere my happens to show up.
Similarly,
He didn't like her because she was successful and talented.
[He liked her for other reasons].
He didn't like her, because she was successful and talented.
[And presumably he wasn't].
In each of the following sentences, there is a distinct shift in
direction between the independent and the dependent clauses: that
is, one piece of information is followed by another, rather than the
meaning of the first clause being dependent on the second. Therefore,
they are separated by a comma.
He threatened to fire me, as if I cared.
She ran for miles, until her legs gave out.
He's never had a job in his life, unless you count that two-week stint as a
taster at the chocolate factory.
She had to hurry to get the house spotless, since the cleaning lady was
expected that morning.
The rule is the same for phrases: Put a comma before a concluding
phrase if the information in it does not directly affect the meaning
of what comes before. In the following examples, each phrase does
not do more than add additional information or commentary to the
clause that precedes it.
She got up to leave, having satisfactorily reduced him to a quivering jelly.
He leaped up from the exercise machine, promptly throwing his back out.
We found her in the washroom, angrily scrubbing the ketchup off her tiara.
They stood by the window, oblivious to the meteor shower raining past it.
He pole-vaulted off the stage and over the fence, leaving his fans howling
in frustration.
The issue of how to deal with phrases and dependent clauses
that lie within independent clauses, rather than before or after
them, is addressed next.
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