By Nicholas Kristof.

WHAT do Bill and Melinda Gates argue about?

Not whose turn it is to wash the dishes or take out the garbage, it seems, but headier stuff. The prospects for eradicating polio. The utility of empowering women. The best ways to save lives.

So what mistakes did they make in their philanthropy? They say they started out too tech-focused.

Oh, and maybe how much to acknowledge to a prying columnist that they sometimes do argue.