It’s impossible to know what went through the mind of Pfc. Ross McGinnis at the moment of decision. He was in Iraq, in a Humvee with four other soldiers. A grenade plopped through the hatch.

His split-second decision, nearly two years ago: Cover the grenade with his body. This week, he was posthumously awarded the Medal of Honor, the military’s highest award for valor.

His parents, Tom and Romayne, received the award during a ceremony at the White House.

The qualifications for this decoration cannot be described with precision. Those approved must display “gallantry and intrepidity at the risk of … life above and beyond the call of duty.”

But it isn’t clear how that differs from the requirements for the next-highest award, the Distinguished Service Cross. That award requires acts of heroism involving “risk of life so extraordinary as to set the individual apart.”

One reason the approval process takes so long is that the military bureaucracy is reluctant to approve Medals of Honor, for fear that a single improper approval would debase previous awards. Fewer than 10 have been awarded since Vietnam.

This provides some context for McGinnis’ split-second decision that day in Iraq in December 2006. As President Bush noted in this week’s ceremony, Ross McGinnis was a dependable friend with an easy sense of humor.

He was, Bush said, the only one in boot camp who could make his drill sergeant laugh. And when the time to choose arrived, he gave everything to save his friends.

He was 19 years old.