On a morning of horrors on Sept. 11, 2001, we witnessed acts of sacrifice that will live forever in American memory.

As people fled the World Trade Center, amid falling bodies and debris, firefighters ran into them. As people ran down the stairs, the firefighters marched up them. They carried 100 pounds of gear, moving slowly toward a fire hot enough to melt steel raging 1,000 feet above them.

After a flaccid decade of (somewhat illusory) prosperity and peace in the 1990s, the savagery of September 11 brought home the timeless relevance of the virtue of courage. Not “moral courage,” but old-fashioned physical courage of the sort celebrated since the days of Homer.

From the firefighters who set out to rescue the victims of al-Qaida’s war on America, to the passengers on Flight 93 who were the first to hit back, to the troops who have waged the fight abroad, it has been a decade of heroes, traditionally defined — men willing to risk life and limb for their country, their mission, their friends.

The esteem with which we naturally hold physical courage is deep-seated. Musing on this, the great English literary figure Samuel Johnson said, “Were Socrates and Charles the Twelfth of Sweden both present in any company, and Socrates to say, ‘Follow me, and hear a lecture on philosophy;’ and Charles, laying his hand on his sword, to say, ‘Follow me, and dethrone the Czar;’ a man would be ashamed to follow Socrates. Sir, the impression is universal; yet it is strange.”

Or formerly universal. We have done much to dumb down courage and make it more accessible through the decades. In his book The Mystery of Courage, William Ian Miller writes of how the definition of the virtue has shifted to accommodate the character of a modern commercial society. “Courage,” he writes, “is thus now held to be what it takes to invest in a Silicon Valley start-up or to vote no on a manifestly weak tenure file.”

If that. Increasingly, Miller notes, courage is used “loosely to congratulate anyone who by his own estimation undertakes some struggle for self-realization.” Search for books on courage on Amazon and you’ll find volumes about business leadership and self-esteem, under such titles as “The Courage to Be Free: Discover Your Original Fearless Self.”

Whatever else they were doing at the Twin Towers, the firefighters weren’t there to discover themselves. Such self-involvement usually breeds the opposite of courage. It was only their commitment to things beyond themselves — above all, their duty — that made them take unbelievable risks outside any calculation of self-interest. 

Moral courage is a real and admirable quality, but our moral heroes are often physically brave, too. Martin Luther King Jr. carried on under the constant threat of assassination. The civil-rights marchers of the 1960s had to be willing to face bludgeons, gas, dogs, and fists.

When there’s a danger — and especially when there’s a war — there’s no substitute for the courage that has been the stuff of legend and of national honors down through the centuries. The brute fact is that most of us aren’t capable of it — for us courage is, in Miller’s words, “a glorious and admonishing phantom.” We can only stand in uncomprehending awe of the acts of the truly courageous.

Why did Jay Jonas and his unit in the North Tower of the World Trade Center, evacuating as it was on the verge of collapse, stop to carry out a distressed woman even though it slowed their escape? Why did a band of passengers on Flight 93 storm the cockpit of their hijacked plane? Why did Jason Dunham, Ross McGinnis, and Michael Monsoor — all Medal of Honor winners from the Iraq War — throw themselves on grenades to save their comrades?

Ask a firefighter such a question and he’s liable to answer, “That’s just what we do.” What we do, in turn, is express our astonishment and gratitude.

— Rich Lowry is editor of National Review. He can be reached via e-mail, comments.lowry@nationalreview.com. © 2011 by King Features Syndicate.