If you are lucky in life, you will have at least one great teacher. More than three decades ago, I had Ed Banfield, a political scientist who taught mainly at the University of Chicago and Harvard University. Ed's recent death at 83 saddened me (which was expected) and left me with a real sense of loss (which wasn't). Although we had stayed in touch, we were never intimate friends or intellectual soul-mates. The gap between us in intellectual candlepower was too great. But he had loomed large in my life, and I have been puzzling why his death has so affected me.

I think the answer -- and the reason for writing about something so personal -- goes to the heart of what it means to be a great teacher. By teacher, I am not referring primarily to classroom instructors, because learning in life occurs mainly outside of schools. I first encountered Ed in a lecture hall, but his greatness did not lie in giving good lectures (which he did). It lay instead in somehow transmitting life-changing lessons. If I had not known him, I would be a different person. He helped me become who I am and, more important, who I want to be.

When you lose someone like that, there is a hole. It is a smaller hole than losing a parent, a child or close friend. But it is still a hole, because great teachers are so rare. I have, for example, worked for some very talented editors. A few have earned my lasting gratitude for improving my reporting or writing. But none has been a great teacher; none has changed my life.

What gave Ed this power was, first, his ideas. He made me see new things or old things in new ways. The political scientist James Q. Wilson -- first Ed's student, then his collaborator -- has called Banfield "the most profound student of American politics in this century." Although arguable, this is surely plausible.

Americans take democracy, freedom and political stability for granted. Ed was more wary. These great things do not exist in isolation. They must somehow fuse into a political system that fulfills certain essential social functions: to protect the nation; to provide some continuity in government and policy; to maintain order and modulate society's most passionate conflicts. The trouble, Ed believed, is that democracies have self-destructive tendencies and that, in modern America, these had intensified.

On the whole, he regretted the disappearance after World War II of a political system based on big-city machines (whose supporters were rewarded with patronage jobs and contracts) and on party "bosses" (who dictated political candidates from city council to Congress and, often, the White House). It was not that he favored patronage, corruption or bosses for their own sake. But in cities, they created popular support for government and gave it the power to accomplish things. And they emphasized material gain over ideological fervor.

Postwar suburbanization and party "reforms" -- weakening bosses and machines -- destroyed this system. Its replacement, Ed feared, was inferior. "Whereas the old system had promised personal rewards," he wrote, "the new one promises social reform." Politicians would now merchandise themselves by selling false solutions to exaggerated problems. "The politician, like the TV news commentator, must always have something to say even when nothing urgently needs to be said," he wrote in 1970. By some years, this anticipated the term "talking head." People would lose respect for government because many "solutions" would fail. Here, too, he anticipated. Later, polls showed dropping public confidence in national leaders. Ed was not surprised.

He taught that you had to understand the world as it is, not as you wished it to be. This was sound advice for an aspiring reporter. And Ed practiced it. In 1954 and 1955, he and his wife, Laura (they would ultimately be married 61 years), spent time in a poor Italian village to explain its poverty. The resulting book -- "The Moral Basis of a Backward Society" -- remains a classic. Families in the village, it argued, so distrusted each other that they could not cooperate to promote common prosperity. The larger point (still missed by many economists) is that local culture, not just "markets," determines economic growth.

What brought Ed fleeting prominence -- notoriety, really -- was "The Unheavenly City." Published in 1970, it foretold the failure of the War on Poverty. Prosperity, government programs and less racial discrimination might lift some from poverty, he said. But the worst problems of poverty and the cities would remain. They resulted from a "lower class" whose members were so impulsive and "present oriented" that they attached "no value to work, sacrifice, self-improvement, or service to family, friends or community." They dropped out of school, had illegitimate children and were unemployed. Government couldn't easily alter their behavior.

For this message, Ed was reviled as a reactionary. He repeatedly said that most black Americans didn't belong to the "lower class" and that it contained many whites. Still, many dismissed him as a racist. Over time his theories gained some respectability from the weight of experience. Poverty defied government assaults; his "lower class" was relabeled "the underclass." But when he wrote, Ed was assailing prevailing opinion. He knew he would be harshly, even viciously, attacked. He wrote anyway and endured the consequences.

This was the deeper and more important lesson. Perhaps all great teachers -- whether parents, bosses, professors or whoever -- ultimately convey some moral code. Ed surely did. What he was saying in the 1960s was not what everyone else was saying. I felt uneasy with the reigning orthodoxy. But I didn't know why. Ed helped me understand my doubts and made me feel that it was important to give them expression. The truth had to be pursued, no matter how inconvenient, unpopular, unfashionable or discomforting. Ed did not teach that; he lived it. This was his code, and it was -- for anyone willing to receive it -- an immeasurable gift.