A wonderful article discussing the need for the comma when a series is being written. A lovely piece. And it is quite readable, too, even for non-English teachers.
it looks like any ordinary comma, and, for the most part, acts like any ordinary comma, except that this comma, plain as it is, does something extraordinary–it guards against the ridiculous.
Commas, much like insults from your significant other’s father, should, if you’re paying attention, give pause. And in doing so, they, by their very design, separate. (My hope is that you’re getting the gist of that as you read this comma-saturated discourse.) The Oxford Comma, specifically, is used before the last item in a series to both separate (thereby denoting equality within the list of items) and to remove ambiguity in the author’s meaning caused by mis-grouped words (eat, cow, and pie, vs. eat cow pie).
Some of your teachers in the past may have told you that the commas separating things in a series simply take the place of all those ands.