Q. Your opinion, please, of the comma in this sentence: “The difference, is affiance.” It is a commercial tagline, so all bets may be off, but one of us has the nagging feeling that there may be a reason for that comma buried in grammar rules of yore. Another of us wondered if the construction is related to “What it is, is football.” Both of us hope you can help sort things out.

A. Sorry—I can’t think of a single reason for that comma. In your football sentence, the comma separates the potentially confusing “is is.” In your tagline, the comma separates a very simple subject from a very simple predicate, and that has long been verboten by the punctuation police.