Most of the talk generated by the recent Democratic debate is about emails or enemies, but far more important were the efforts of the presidential candidates to explain what they would do about achieving another e-word: equality. More to the point, they talked about the problem of "inequality," a word used eight times by the candidates and once by the moderator. And when they spoke of inequality, it was clear that their concern was the accumulation of wealth and power by the very wealthy.

Inequality is on everybody's lips these days — everybody on the left, anyway, and a lot of people in the center and on the right as well. But what if everybody's wrong? That's the contention of "On Inequality," a small, smart new volume by Princeton University philosopher Harry Frankfurt. At the very beginning, he states a simple but powerful thesis: "Our most fundamental challenge is not the fact that the incomes of Americans are widely unequal. It is, rather, the fact that too many of our people are poor." Progressives, in other words, are shooting at the wrong target. The moral problem posed by the distribution of wealth isn't inequality. It's poverty.

These might seem like the same issue, but Frankfurt shows us with elan that they are not. Suppose, he says, there is a resource that will keep a person alive, but only if that person has five units of it. There are 10 people, and there are 40 units of the resource. If the resource is distributed equally, everybody gets four units — and everybody dies. To insist on equality in that case, he argues, "would be morally grotesque."