Editor's note: Gene Seymour is a film critic who has written about music, movies and culture for The New York Times, Newsday, Entertainment Weekly and The Washington Post. The opinions expressed in this commentary are solely those of the writer.

(CNN) -- Most of the shock that resounds after hearing that Robin Williams died Monday comes from its utter implausibility. How could Robin Williams, of all people, just stop breathing, moving and, most of all, talking?

It's as though we've been told the moon spun out of orbit or that water no longer boiled, or froze, at the proper temperature. If Robin Williams is dead, then light no longer refracts, atoms no longer bond and gravity has gone out of business.

Yes. It's that implausible.

For many of us over the last 40 years or so, Robin Williams was an irresistible force of nature that nothing, not even the demons in his head or the sometimes regrettable consequences of their actions, could stop. If his motor ever ceased running, even for a second, his audiences rarely noticed it. They just stayed on the edge of their seats awaiting the next eruption, and were never disappointed by whatever inspired lunacy burst forth.

Practically from the beginning, when we first saw him turn scripts from the 1978-82 ABC sitcom "Mork and Mindy" into staging areas for unalloyed free-form verbal jazz, Williams seemed in supernaturally perfect command of all the voices in his head.

Whether delivering stand-up comedy or an introduction at a testimonial dinner, Williams could make a casual digression into a stream-of-consciousness lick worthy of William Faulkner, James Joyce or any surrealist you can name.

Where did he ever come up with THAT, we always wondered, whether it was a reference to an old movie we'd thought we'd forgotten or a side-swiping barb at a politician, or even something embarrassing about himself.

Patients remember Williams as 'comedic Mother Teresa'

His own rueful experience with addiction drew from him one of the greatest quotes ever about drugs: "Cocaine is God's way of saying you make too much money." Or the one about how alcohol abuse can get so out-of-control, "you'll do things that'd make the Devil say, 'Dude...'"

Someday soon, if it hasn't already happened, there will be a collection of such aphorisms, which at times approached the trenchant pithiness of Mark Twain or Oscar Wilde. The problem with remembering all of them now is that they were all but lost in the ack-ack fire of Williams' spontaneous inventions. Even when he stood still, you could almost feel the waves of energy struggling to break free. The way he contained those waves reminded us that his was a mind, paraphrasing Albert Camus, that always kept itself in check.

And besides, good actors can always make silence and space work to their advantage. Imagine our surprise when it turned out that this most formidably intellectual of his generation's comedians was also a very good -- and, at times, great actor. He channeled his high-octane inventiveness into creating indelible and endearing movie portrayals as the hip GI disc jockey in 1987's "Good Morning Vietnam," for which he received the first of his three Oscar nominations for best actor.

I thought he should have won for playing a grief-mad widower in 1992's "The Fisher King," but Hollywood showed how much they loved him by giving him the best supporting actor Oscar in 1998 for playing an emotionally wounded psychiatrist in "Good Will Hunting."

For whatever it's worth, the Robin Williams movies I most enjoyed were the ones where he took chances and/or let fly. This would, for me, exclude his title role as "Mrs. Doubtfire" (though I understand why so many cherish its memory), but would include such wildly varied work as his supersonically spritzing genie in 1992's "Aladdin"; his underrated star turn in the underrated 1980 musical "Popeye"; and, among his riskiest performances, the portrayal of the clammy, anxiety-ridden hustler Tommy Wilhelm in the 1986 TV movie version of Saul Bellow's "Seize the Day."

In all his roles, playing crazy or cute, good or evil, sagacious or sanctimonious, Robin Williams always showed you his considerable empathy, not just for the people he rendered, but for the audience; the same audience he sought to conquer, if not overpower, with his free-range comedy routines where, as with his friend and mentor Richard Pryor, he was most vividly and resoundingly himself--with all his foibles, grievances, fears and desires.

We thought we'd be able to call upon his compassion, his intelligence and his energy for as long as there was air and water. Is Robin Williams really dead? What on Earth will the weather be like tomorrow without knowing he's still around?

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