As everyone who was in the area remembers, September 11, 2001, was a clear, shining day. Not so memorable, perhaps, is what it was like to live in the world before the iPhone. My wife, Susan, and I were even less connected, having eschewed television. Thus, when I drove her to physical therapy at St. Francis Hospital in Poughkeepsie, we knew not what was going on.

I left her there and headed for Marist College, where my ethics class was meeting at 9:30. I had turned on the radio, and soon learned that a plane had flown into a building in New York City. (I think now that it was the second plane.) Although the drive was short, I heard enough to reckon this was going to be big.

My students were all there, ready for class (as ready as college students can be at 9:30 in the morning). I had decided to say nothing about the planes. They said nothing about them—if they knew. We had a normal class, which is my instinct: Class time spent on the timeless is worth more than timely discussion in the long run (and we would have been speculating without any knowledge at that point). At the end I told them something had happened that morning, something closely connected to ethics, and that we would be discussing it when we met on Friday.

I joined my wife for the end of her therapies, and we spent the rest of the day in that odd quiet space that I’ve oft imagined is like the eye of a hurricane. The skies were clear: There were no jet streams to be seen streaking across the blue. Our high-school daughter got the news in chemistry class, which was interrupted as they listened to the radio. She remembers praying, especially for a friend whose father worked in the city. Still, school went on. That evening she had her usual ballet class. It seemed appropriate not to let this change our routines. Just three days before, our son had flown JFK to LAX on American Airlines. He phoned from college, when he could get through, glad to hear our voices.

People responded in different ways and on differing time schedules, but the impact of those planes was upon everyone. A year later I was doing a funeral for a young doctor whose body was never found: The service lasted two hours, the church was filled, and hundreds were standing close by. This, in a village three counties north of New York City.

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My ethics class was different that semester. My students had the acquired reflexes to think in relativistic terms. About some ethical claim, they would say, “That might be wrong for you, but for someone else it could be right.” They had been trained to be sensitive to people who had different opinions and beliefs; and indeed, it is a good thing to try to get inside other peoples’ minds, to see things as they do.

However, for the rest of the fall of 2001, whenever someone would make a relativistic comment, another student would say: “But flying those planes into the Twin Towers was wrong.” Something new in our lives had happened: We had seen a horror perpetrated on a large scale not far from home. We had a point of reference for something that was wrong, period.

This window into what moral theology calls intrinsic evil did not last, of course. By the following term the shock had waned, and their reflexive relativism was back. Students then said, “The men who flew into the buildings thought they were doing right.” But for the first three months after 9/11, no one would have said that without going on to say, “Yet they were, in fact, wrong.”

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In moral reflection upon warfare, there is a tradition known as “just war thinking.” It is better, I believe, not to call it “just war theory” (as it is usually referred to) for it is not a theory so much as a body of reflection on how the search for justice can play out in war. Francisco de Vitoria (1483–1546), one of my heroes, was a Dominican who taught at the University of Salamanca in Spain. In his lectures he gave voice to what we call the principle of discrimination: One should never aim at killing innocents in war. One is to discriminate between combatants and noncombatants, and only against the former may one aim one’s attack. Over the centuries this principle has been refined and is codified now in international law.

This is an important principle. What we saw on September 11 was horrible because its deliberate aim was to kill innocents. This also is why abortion is wrong: An innocent child is killed. And it is why euthanasia is wrong: It aims not at healing or comforting a person but at his or her death. To make this contemporary, it is why we should feel revulsion at the pictures of hospitals and apartment buildings willfully bombed in Ukraine.

We need to resist the impulse to revert to relativism in our thinking. Some things really are horrors. And even if they are being carried out by people who think they are doing right, those things remain wrong.