Journalism professor Don Ranly wraps up his three-part series on the most common punctuation mark
It’s time I finished my ranting about commas. I promised you eight nearly infallible, always usable rules, and so far I have delivered only five of them.
Let me state those five once again before I go on:
If you missed the explanations for these guidelines, you can find them in the Ragan archives.
Now the next rule is a bit more arbitrary. You won’t find it written down in many places, but it’s a good one for editors to follow. Let me preface it by saying that some editors, to be consistent, say that you should place a comma after every introductory prepositional phrase. You can adopt that practice if you want, and no one can cite you for an error. Do you think a comma is necessary in this two-word introductory prepositional phrase?
Example: In Chicago, it snowed yesterday.