I don't know anyone who wasn't in some kind of a fog during his or her own wedding ceremony. Till death do us part? For richer or poorer? Promises that came effortlessly and joyfully in the middle of the night become paralyzing when stated before the unblinking gaze of an officiant and your new in-laws. Most of us tune in only enough to perform simple verbal repetition.

We get married publicly so that other people are there to witness our vows. To hear the words along with us, if not for us. Even people who get married drunk by an Elvis impersonator have a witness. We get married in view of a community. Marriage is a public act.

And so is the end of a marriage. The breakup of a marriage can send a ripple effect of devastation and fear through the surrounding community, causing everyone in its path to recontemplate what it is that marriage means or doesn't mean to them.

In "Dinner With Friends," when one of the husbands leaves his wife for a younger woman, his act sends another couple reeling as well.

Donald Margulies searingly depicts this very phenomenon in his play "Dinner With Friends," which won the Pulitzer Prize for drama on Monday. The play focuses on four friends--two couples, both married for about 12 years. When one of the husbands leaves his wife for a younger woman, his act sends the other couple reeling as well.

Some months after the breakup, the two men meet for a drink in a Manhattan bar. Gabe, the faithful husband, notices that Tom looks well, that he's lost weight. Tom is happy, eager even, to offer his diet tips, which of course he attributes to his new 24-year-old girlfriend. "Nancy and I, we get up at six, run four or five miles, come back, make love in the shower," he says. "That's my new regimen. And let me tell you: It's totally changed my perspective on my day!"

Tom goes on. He wants Gabe to know about Nancy's sexual imagination, daring, and wisdom. His former wife "was never at home in her own body," he says. "And then once the kids came...well, you know how that is."

Tom's comment hangs in the air for Gabe to absorb. And as Gabe silently sops up the implications about marriage in general, and his own marriage in particular, Tom raises the stakes. By ending his marriage, he's saving his own life, he argues, and also providing a valuable lesson for his kids: "What kind of example would I be setting for my kids if I stayed? That we're all too powerless to change our lives?"

This is a tough argument. Who likes to argue the anti-growth, pro-inertia position against new sex positions in the shower? Few of us would counsel a good friend to stay in a marriage that had clearly rotted to the core and was bringing no happiness to anyone. But when does one abandon ship? Anyone who's been married for any length of time knows that marriage is all about hanging in through rough times, sometimes through agonizingly rough times, and then emerging, in varying degrees of scathe, to an altered and often reinvigorated marriage.

In response to Tom's provocation, Gabe can only spout truisms about mortality: "It all goes by so fast," he says. "The hair goes, and the waist. And the stamina... Want to hear a shocker? Karen is pre-menopausal. That's right. My sweetheart, my lover, that sweet girl I lolled around with on endless Sundays, is getting hot flashes. It doesn't seem possible."

Who likes to argue the anti-growth, pro-inertia position against new sex positions in the shower?

Lame as it may sound as a counterargument, Gabe's reply is stunningly sufficient. People who go around defending marriage--like the authors of the Defense of Marriage Act, which denied recognition of same-sex marriages, or of California's recently passed Proposition 22, which gratuitously seconded that denial--come off sounding either like paranoid authoritarians or like bigots.

On the other hand, people who go around defending the supremacy of bachelorhood often sound equally strident. Bill Maher, TV talk show host and human billboard for non-commitment, recently took on a trinity of marriage promoters-a rabbi, a priest, and, for some reason, the MTV personality Kennedy.

Maher's arguments were aggressive and pithy: Don't tell me you know what's best for me. I like having a string of exciting conquests--no one can tell me my life's not fulfilling. A relationship is like a plane, and sex is the fuel. Once you run out of fuel, you crash. With their counterarguments about true peace, selflessness, and contentment, the priest, the rabbi, and Kennedy sounded like judgmental drips, or cult members.

When Gabe suddenly offers up the fact that his wife is pre-menopausal, his remark conveys the awesome quality of facing our own mortality with another human being. Gabe's awe is ineffable and beyond argument; it just is. And there's the great irony inherent in anyone's defense of marriage--and what makes it in no need of defense. It is performed publicly. Its end has public consequences. But its meaning is as private as the meaning of life itself.