Marshall McLuhan said the only advertising that people pay attention is for products they already own. Errol Morris, who has a fascinating new book questioning the decades-old verdict in the Jeffrey MacDonald trial, believes in a "confirmation bias." In other words, we look for and see things that confirm what we already believe.

I thought about this when I read a recent article by Gwen Ifill. Ifill, who has almost as much experience with presidential debates as a candidate, has an interesting analysis which debunks  the "myths" of these encounters. Some of her rebuttals are irrefutable: No, the candidates don't see and approve the questions in advance, but, I might add, the debate-prep teams predict about 90 percent of the questions. It's not unlike a final exam; if you study, you are rarely surprised by a question. And, yes, I agree with her that the moderator's job is not to argue with the candidates or counter their mistakes; that's their province. 

But Ifill has some other more provocative points. Basically, she argues that debates have little or nothing to do with voter choice. Ifill makes the "confirmation bias" point; voters watching the debates have already made up their minds and see what reinforces their choices. And she argues that even memorable debate moments, Lloyd Bentsen schooling Dan Quayle, George H.W. looking at his watch, rarely matter to the ultimate outcome.

While Ifill makes some interesting points, I think she makes a bit too much of them. Debates certainly don't sway masses of voters, but they don't have to be decisive. And Ifill confines her analysis to the debates themselves; many voters will be influenced not just but what they see in the debates but what they hear in the analysis that follows. In fact, the debates might matter more than ever. In an age when so many voters have already made up their minds, any opportunity to communicate without filters to undecided voters is vital.