(Luke Macgregor/Bloomberg)

Robert Hughes is the author of "Walker Finds a Way: Running Into the Adult World with Autism."

At Christmastime in our house, the Holiday Prohibitions go into effect. Recently, I made the mistake of meekly testing a rule, almost whispering, "Hark the herald angels sing / Glory to the . . . "

"No newborn king today!" my 32-year-old autistic son shouts from across the living room, smiling but wary.

"Peace on Earth and mercy . . . " I continue, louder now, more out of mischief than anything else. And Walker — all 6-foot-3 and 210 pounds of him — lunges across the room, puts his hand under my chin and shouts, "No mild today!" He's laughing and blushing, his face lit up with a grin. But he's not having any of this Christmas singing stuff. No way!

So much about Walker is right here in this almost-conversation: He loves me and likes the teasing. He speaks, a little, but not with normal phrasing, and certainly delivers no "opinions" as we normally think of them. He's vigilant, responding instantly to whatever is happening, especially anything his father does. He knows his Christmas carols and in fact could finish any line of any one of them. And known to me and his mother but not to many others, he would love to sing with his dad, except he would find the experience to be so emotionally momentous, to cause such a high-in-the-Richter-scale shaking of the soul, that it could not be borne.

He can seem like a huge toddler sometimes, demanding close attention moment to moment. Outdoors, he might run into the street if I'm not holding his hand. In a grocery store, he might grab a fistful of nuts and jam them into his mouth. And anywhere at all, he's likely to startle the citizenry by bellowing, "I want pen!," his signal to me to write our agenda for the next few hours on one of the note cards I keep in my pocket. His mother and I have never taken him on a plane, mainly to avoid turning up on the nightly news.

This seeming toddlerhood is extra-ironic, for he is also a dazzlingly handsome and charming man. In a still photograph, he looks like a world- ­beater from central casting. Looking at him as he sits on our couch, legs crossed, head resting on his hand, I can have microsecond "my son the neurosurgeon" fantasies.

And get, momentarily anyway, pretty grim.

When he was an actual toddler, he was the ultimate Christmas kid. One moment stands out. At a holiday party, Walker and I performed "Winter Wonderland" loudly and clearly and proudly. But as he grew older and low- ­functioning autism calcified around his life, he spoke less and sang less. Unable to join in the family chatter, he had to take in all the music, smells, lights, color and beauty of the season while silently battling whatever it is in his head that distracts him from our "normal" world. When young, he couldn't see his favorite holiday films often enough; now most Christmases they get the "No movies today!" treatment.

Every day, I see how the ability to say what's on his mind would protect him a bit from his many fears, yes, but also from what looks like a kind of uncontainable hyper-joy. Robert Graves got it right in his poem "The Cool Web." When we're very young and not talking yet, he says, the world is sheer magic. Then words and sentences step in to tamp the ecstasy down: "There's a cool web of language winds us in / Retreat from too much joy or too much fear."

This is why Ellen and I never give up on the language quest with him, and why he never gives up, either. The ability to make simple remarks about what's on his mind — "This place is too noisy, Dad. Could we leave?" or "Let's get out of the house and see a movie" or even "Are you kidding? 'National Lampoon Christmas' again?" — would expand his life immeasurably.

But, contrary to so much written about autism, his mother and I know him to be empathetic, intelligent and blessed with a knack for signaling the people in his life that he loves them. He doesn't let the maddening absence of sentences get in his way.

So when his "No mild today!" comes and he blushes and laughs and grins, I may not get the duet performance I want, the bonding of father and son in a Hollywood holiday film. But his message comes through to me with the clarity of church bells on Christmas morning: "Yes, I remember singing that one, Dad. What fun we had! It's just too much for me to take in right now, but thanks for reminding me of it."

It's not "conversation," but for me, in the truest and warmest and liveliest sense, it's more than enough.