Harvard economist Greg Mankiw’s provocative recent paper, “Defending the One Percent,” has reinvigorated the debate about taxing the rich across the economics blogosphere, with Paul Krugman, The Economist and other prominent voices weighing in.

Interestingly, Mankiw’s paper is not even about economics per se. It’s mostly a treatise in moral philosophy. The eminent economist even acknowledges that his field of expertise faces profound limitations when it comes to devising tax policy, writing that “No amount of applied econometrics can bridge” the “philosophical divide” over what constitutes a fair system of taxation. “It is useful to keep in mind,” he cautions, “when we are writing as economists and when we are venturing beyond the boundaries of our professional expertise.”

I don’t agree with the policy thrust of the paper, which, as you might expect from the title, is an extended argument against progressive taxation. But I applaud Mankiw’s recognition that even the shrewdest charts, graphs and equations will ultimately be unable to resolve what is fundamentally a moral question.

So Mankiw’s paper isn’t just brief for one percent. It is, inadvertently, a powerful defense of the value of disciplines like philosophy, civics, and the humanities more broadly — disciplines which, the American Academy of Arts and Sciences noted in a widely publicized report released last week, have declined dramatically in American education.

A tide of quantification is sweeping over almost all human endeavors — from basketball statistics to NSA surveillance and everything in between. Our politics also reflect this trend. The new kings of the political blogosphere are economists and wonks who produce graphs and datasets to support their arguments. In the 2012 presidential debates, Barack Obama and Mitt Romney cited reams of statistics and think tank studies.

Often, the trend toward quantification clarifies and sharpens our political debates. For example, UC Berkeley students created a website last fall that allowed voters to see the exact financial impact of the presidential candidates’ tax plans on their finances. But the proliferation of data can make it easy to forget that the most vexing public policy challenges — from taxation to affirmative action — are questions of morality, not math.

In the last week, commentators have tried to stress the role of the humanities in personal fulfillment. David Brooks, for example, wrote that “the job of the humanities” should be to “cultivate the human core, the part of the person we might call the spirit, the soul.”

In my view, however, the humanities have an even more important role — to provide moral, historical and philosophical insight into our politics. On the really big issues, as Mankiw rightly suggests, philosophy trumps pie charts.