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There’s a question that’s been bugging me for nearly a decade. How is it that half of America looks at Donald Trump and doesn’t find him morally repellent? He lies, cheats, steals, betrays, and behaves cruelly and corruptly, and more than 70 million Americans find him, at the very least, morally acceptable. Some even see him as heroic, admirable, and wonderful. What has brought us to this state of moral numbness?

I’m going to tell you a story that represents my best explanation for how America has fallen into this depressing condition. It’s a story that draws heavily on the thinking of Alasdair MacIntyre, the great moral philosopher, who died in May at age 94. It’s a story that tries to explain how Western culture evolved to the point where millions of us—and not just Republicans and Trump supporters—have been left unable to make basic moral judgments.

The story begins a long time ago. Go back to some ancient city—say, Athens in the age of Aristotle. In that city, the question “How do you define the purpose of your life?” would make no sense. Finding your life’s purpose was not an individual choice. Rather, people grew up within a dense network of family, tribe, city, and nation. They inherited from these entities a variety of duties, responsibilities, and obligations. They also inherited a social role, serving the people around them as soldiers, farmers, merchants, mothers, teachers.

Each of these social roles came with certain standards of excellence, a code to determine what they ought to do. There was an excellent way of being a warrior, a mother, a friend. In this moral system, a person sought to live up to those standards not only for the honor and money it might bring them, but because they wanted to measure up. A teacher would not let a student bribe his way to a higher grade, because that would betray the intrinsic qualities of excellence inherent in being a teacher.

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By being excellent at my role, I contribute to the city that formed me. By serving the intrinsic standards of my practice, I gradually rise from being the mediocre person I am toward becoming the excellent person I could be. My life is given meaning within this lifelong journey toward excellence and full human flourishing.