If you want to see someone look at you as if you’re crazy, try wishing him “Merry Christmas” on Dec. 26. I made the mistake of doing this once with a toll collector on the Mass Pike. You’ll be greeted as if you were Rip Van Winkle just woken up from a nap. “Hey, buddy, don’t you know that Christmas was yesterday? Have you lost track of time?”

But in fact Christmas is a season, not a day. The season of Christmas this year is a full three weeks long, from Christmas Day to the feast of the Baptism of Our Lord, on Jan. 13. And “Merry Christmas” is the proper greeting for every day in that season.

So Merry Christmas to you! (Not a Merry belated Christmas!) As you read this now, think: the Church is celebrating Christmas today just as much as it did on Christmas Day. (And think also: Am I still celebrating Christmas?)

The world testifies to this indirectly. It knows that Christmas is a season, only its season begins earlier and ends on Christmas Day. Perhaps merchants are getting desperate and worry that Black Friday will one year be red rather than black. But their season -- call it Pseudo-Christmas -- seems to begin earlier each year.

In our family we have a tradition called “First Carol Sighting” of the year. The game is to be the first to hear a Christmas Carol on the radio. It used to be that there would be no carol sightings until after the Thanksgiving turkey had been picked clean and turned into soup. But this year my wife won the game with a sighting of “Silver Bells” on Nov. 10!

Pseudo-Christmas is now 6 weeks long. If you began celebrating Christmas on Nov. 10, it’s no wonder if you’re tired of the whole business and couldn’t possibly continue to celebrate it now. But the world has things backwards. The time leading up to Christmas belongs to a different season, Advent, which the old books used to call a “minor penitential season.”

Advent in theory is like Lent, only milder. It’s shorter -- four weeks instead of six -- and the penances one adopts are less stringent. In Advent one doesn’t “give things up” so much as “take things on,” such as small, thoughtful acts to help prepare oneself for the arrival of the Christ child.

In anticipation, the austerity of Advent inevitably gives way to celebrations as Christmas approaches, even in the strictest Catholic households. Offices and schools will necessarily hold parties before the Christmas holiday. The Church herself encourages these early rehearsals of the great feast with her holy day of the Immaculate Conception, which always falls squarely in Advent. Nonetheless, these should be “exceptions which prove the rule.”

Some overly pious sorts complain about the commercialization of Christmas. But the tasks of shopping and wrapping can pose no obstacle to holiness whatsoever if they are located, as they should be, in a “minor penitential season.” Think of Advent as a time of mortification, and then Christmas shopping, and even enduring Christmas carols in November, are so many aids to your becoming a saint.

The world celebrates Pseudo-Christmas for the time of Advent, and then, when Christmas actually begins, it acts as though there never was a Christ. This year necessity, and more guests than had been expected, obliged my wife and me to take a trip to the grocery store on the afternoon of Christmas Day. We discovered that all of the offerings and decorations associated with Christmas were already gone. It was Christmas Day, for Pete’s sake, and yet the aisles of Christmas panettone had been cleared away and replaced by stacks of champagne bottles in readiness for New Year’s. You couldn’t find a garland or reindeer in the entire store.

But this makes sense and should disturb us only if we expect grocery stores to be aids to celebrating Christmas. Pseudo-Christmas is based on consumer demand, or need, which is always anticipatory: once need is satiated, it no longer exists. But Christmas itself is based on a gift received, which is enduring.

If the world can celebrate its shadow “holiday” for six weeks, can’t we celebrate the real thing for three? Has your Christmas tree been tossed curbside already? Are your lights put away in boxes? Have you not played a Christmas carol since Christmas Day? In short, have you let grocery stores and shopping malls dictate for you the rhythm of Christmas? Rather, your family, which is a “domestic Church,” should take its cue from your parish church, which still has its crèche and tree.

Not that we don’t need at least three weeks to ponder what Christmas means. If you think it’s easy to grasp, you probably don’t get it. The humility of God born in a stable? The implications of a God who spurns the trappings of power and acclaim? That our greatest good is a gift, not something we earn? That we are invited into the Holy Family? What about our being asked simply to meditate on the beauty of the human form of the Christ child and his mother?

People sometimes lament the fact that Christmas lasts only one day. “Why can’t every day be Christmas?” they say. It can -- and given the Eucharist, God with us, it definitely is -- but for ourselves we have to start by at least making Christmas three weeks.

Michael Pakaluk is a visiting professor of philosophy at the Catholic University of America.