One of the reasons for the wild popularity of the television series "Mad Men" was that it portrayed in sublime detail the brief period in which America was fun for many people and not quite so politically correct. We can shrug at the cigarettes, booze and sexism; we know better now. Some secretly may covet one or another of those vices, but the remarkable sight is of prosperous white people enjoying themselves without fear of scorn.

All ages have some form of conventional wisdom, but in the "Mad Men" era, a lot of life was laissez-faire. The young president of the United States shared some of their diversions, but the public didn't need to know. What a time that was.

But times change. And I came in time to learn that conventional wisdom is always changing. This was my major inheritance, and it's priceless. And the gift came from my father.

Families back then ate dinner together. Every single evening. In our comfortable home in Minneapolis, we all gathered at precisely the same hour each day. Two parents, four children. Each person's place was always the same; the table was round, but where my father sat was undeniably its head.

Three of the children were old enough to make trouble for him, and the fourth was getting there fast. The conversation was lively and general; the topics of the day were savored as avidly as my mother's magical meal.

My father was a mild-mannered man. I never heard him raise his voice. But when it came to Right and Wrong, he could not be moved. At least, he never was moved by us. His offspring ceaselessly shared the platitudes of the day, but every volley was returned. Not harshly, nor really with argument. What he thought was wrong, he simply rejected. He seldom got beyond "I don't think so," or "I don't believe it." But he never, ever gave in.

He was always outnumbered, as his progeny tended to stick together. But there was maddening futility in our assaults. He seemed completely unaware that the subject under discussion was worth feeling strongly about. He returned each serve with equanimity, as his children grew increasingly incensed. How could he not see reason?

I see now that what we regarded as "reason" was simply the fact that everybody else agreed on the point we were making. My father didn't care what everybody thought, and he didn't even seem to know who "everybody" was.

The night we thought we had him was when he took a particularly large slice of roast beef — his second helping. There was a lot of fat on it.

"Be careful, father," I said. "That's not good for you."

"Why not?"

"It has a lot of cholesterol."

"So?"

"Cholesterol is bad for you."

"Who says?"

"Everybody knows that."

"I don't."

"It's been proven!"

"By whom?"

"By Ancel Keys."

"Who's he?"

"A professor at the University of Minnesota. He also invented K-rations!"

"That was good?"

"He got his picture on the cover of Time."

"So did Hitler."

"He's proved that animal fats cause heart disease! Proved it!"

"Not to me."

He was, throughout this exchange, enjoying his second large helping of roast beef. He wasn't trying to make a point. He liked that food. (So, for that matter, did we — you couldn't tell which side the combatants were on from their plates.)

My mother never joined in these discussions. At the dinner table, she said little and ate little. She watched attentively to see that everyone else had enough. She smiled, and sometimes nodded, at each remark that was made, regardless of who made it. Her look was always one of approval that somehow assumed we were enjoying ourselves.

"Father, I'm only concerned about your health. I want you to live a long time. So stop eating cholesterol!"

Then, like a judge leaning forward on the bench, he placed his silverware on the plate. A ruling was at hand.

"Over the years," he said, "I've heard that a lot of things are bad for you. And sometimes what you heard turned out to be wrong. And then there was always something new that was bad for you. Maybe this cholesterol thing is overrated."

Now, more than 50 years later, the new consensus is that Dr. Keys had used flawed data. His study is now seen as a famous mistake. When my son graduated from medical school a few weeks ago, the commencement speaker singled out the Keys study, and his tone was derisive. The jury seems to be in, and it has sided with my father.

And I'm glad that he was right. Even when opposing him, I was beginning to see that skepticism was a virtue. I increasingly came to make use of it myself.

So, after a lifetime of doubting the wisdom of the moment, I want to thank my father. I hope he hears me, wherever he is.

"Who knows?" he would have said.

David Lebedoff is a Minneapolis attorney. His most recent book is "BUZZ."