Commas That Matter
Lists, intro phrases, and joining sentences
Commas have a scary reputation, but you only need three rules to handle most real-world writing. Everything else is fine-tuning.
Rule one: commas separate items in a list. Before: We need coffee milk sugar and cups. After: We need coffee, milk, sugar, and cups.
That last comma before and is called the Oxford comma, and some styles skip it. Using it is never wrong, and it prevents genuine confusion, so this course recommends it.
Rule two: put a comma after an introductory phrase, the warm-up before the main sentence starts. Before: After the long drive we finally relaxed. After: After the long drive, we finally relaxed. The comma tells your reader: the setup is done, here comes the point. Short intros (like Today or First) can sometimes skip it, but including it is always safe.
Rule three: use a comma before and, but, or, so, for, nor, or yet when they join two complete sentences. Before: I wanted to call but it was too late. After: I wanted to call, but it was too late. Quick check: could each half stand alone as its own sentence? If yes, add the comma. If not (I wanted to call but forgot), no comma needed.
One habit worth unlearning: the idea that a comma goes wherever you would pause for breath. It is close to true, but it leads to commas between subjects and verbs. Before: My favorite coworker, brings donuts on Fridays. After: My favorite coworker brings donuts on Fridays. Never split a subject from its verb with a single comma.
Recap: commas separate list items, follow introductory phrases, and team up with joining words (and, but, so) to connect two complete sentences. When in doubt, ask what job the comma is doing. If you cannot name the job, it probably does not belong there.