When my older son — a kind and gentle soul — started out in sports, he had less than a killer instinct on the field.

We worked on playing more aggressively. Finally, one game, I saw him execute the most beautiful open-field block ever. He absolutely leveled his man.

Unfortunately, it was a soccer game, not football.

For some inexplicable reason (temporary blindness? disbelief that the kind and gentle soul really did just launch another kid into low-Earth orbit?) the referee didn't call foul. We had a little conference afterward, in which praise of his newfound warrior spirit was joined with some judicious counsel on the finer points of playing the ball, not the man.

The principle applies beyond the soccer field. If a person values truth and reason, he always argues the argument, not the person making it. Two plus two is four even if the guy who says so drinks too much and kicks little puppies. And five is the wrong answer, no matter who gives it — hero or villain, on our side or the other.

Too many of our public and private debates play the man, not the ball. If winning is everything and truth is optional, that can be brutally effective. But if you care about truth — and the democratic idea that people of good will can reason together — then it's not enough to make others think the other man is so awful he must be wrong. You need to be actually right yourself.

The political philosopher John Stuart Mill once wrote something that modern politicians and pundits, indeed all of us, should take to heart:

"He who knows only his own side of the case knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side, if he does not so much as know what they are, he has no ground for preferring either opinion.… Nor is it enough that he should hear the opinions of adversaries from his own teachers, presented as they state them, and accompanied by what they offer as refutations. He must be able to hear them from persons who actually believe them … he must know them in their most plausible and persuasive form."

I once had the pleasure of watching a famously no-nonsense judge of the Orange County Superior Court obliterate a string of lawyers who could have used Mills' good counsel. One after another, they got up to argue against not their opponents' actual positions, but subtly different ones, easier to refute.

You'd think that after the heads of the first few came rolling figuratively down the aisle, those following might have gotten the message. But no — they kept marching up to the stand, trying to blow something past the judge, and getting mowed down, one after the other.

That maneuver only works on dimwits or, more commonly, people who already agree with you and just want their bias reinforced. Our judge was rightly insulted at the implication he was either.

As John Milton wrote, "Let [Truth] and Falsehood grapple; who ever knew Truth put to the worse, in a free and open encounter?" The only proper responses to an argument we dislike are a better argument, if we have one, or review of what we thought we knew.

How many of us can say that we arrive at our opinions after giving a truly fair hearing to both sides of the case? Do we accept or dismiss a person's views automatically because of who we're told he is — pro-this or anti-that, liberal or conservative, credentialed or insufficiently so?

If we can't answer a challenge to our views, do we reconsider — or do we try to get the challenger shouted down, or ignored or fired? Do we strive to examine opposing views "in their most plausible and persuasive form," or do we — like the drunk looking for his keys by the lamppost because the light's better there — distort them into something more easily dismissed?

Do we play the man, or do we play the ball?

THOMAS EASTMOND practices law in Irvine and lives in Newport Beach.