If you read "Bob, a DJ and a clown" on a guest list, are three people coming to the party, or only one? That depends on whether you're for or against the Oxford comma- perhaps the most hotly contested punctuation mark of all time. When do we use one? Can it really be optional, or is there a universal rule? TED-Ed explores both sides of this comma conundrum. [3:25] L.11-12.1a Gram/Usage changes, L.11-12.1b Usage issues