If you’re looking for a grammatical convention guaranteed to spark an unnecessarily outraged debate, look no further than the Oxford comma [Editor’s note: I don’t know that I’d call it unnecessary].

This lavishly researched book shows that dots and dashes are an essential component of style, whether you’re a medieval monk or Donald Trump ...

Use a comma to separate two independent clauses when they are joined by one of seven coordinating conjunctions (for, and, nor, but, or, yet, so). We were out of ice cream, so I went to the store. (c) ...