This presidential election is a battle between two visions of fairness, embodied in President Obama's "You didn't build that" speech and Mitt Romney's disdain for "the 47%." Both candidates believe that tax rates on the rich must be changed to restore basic fairness and revive the American Dream, yet they plan to move those rates in opposite directions. The only way to make sense of these opposing strategies is to realize that there is more than one definition of fairness. In fact, there are three basic ones, and liberals and conservatives differ on which they value most.
1. Proportionality
Proportional fairness...