OFTEN YOU NOTICE that style changes substance out of all recognition, and it is hard to say (so great is the impact of the style) the substance is still the same.

This is a central crisis in all writing, of course. Nobody seriously argues that a Shakespeare play is "the same thing" as the story on which it was based, because the style has so transformed it.

It is also a question in life, in the judgment of reality itself, and here is an example (drawn from architecture) of style transforming substance beyond recognition.

Everybody knows the Pantheon at Rome, the vast temple to all the gods, with a dome 130 feet in diameter and 140 feet high, so vast that the people look like ants crawling.

Suppose you take that vast diameter and reduce it to a fourth or a fifth its original dimension. And then suppose you alter the pitch of the pediment, and play about with the proportions of height to width in the portico, and change the building from monotone concrete to red brick trimmed in dazzling white. And add a few fancy mouldings here and there, contrasting with the main fabric. And raise the whole thing up on a platform and a set of monumental stairs. And cut six dazzling white windows against the red brick in front. And run Chippendale railings around the parapets and flank the whole thing with an avenue of lesser buildings and a few hundred little Tuscan columns of white plaster, and a lawn of green grass in terraces?

You still have (as the fanciers of substance love to insist) the same substance -- the dome, the pediment and columns, the drum and its thrust on the walls.

But the style fanciers say no. The changes have been too great.

For 40 years the Rotunda of the University of Virginia has bothered me, since everyone (including its architect, Thomas Jefferson) swears it is based pretty faithfully on the Pantheon at Rome.

And yet, in the 34,619 times I viewed the Rotunda it never looked to me remotely like the Pantheon, and I could not think why.

I now believe it makes a difference -- and not a superficial difference but a substantive one -- if you reduce the diameter of a dome by 75 percent for starters.

Now as far as I am concerned, Jefferson is the big glory of America, and he is certainly as irresistible an architect as anybody can imagine, despite his trifling flaws. He is incompetent at handling interior space, he uses mouldings theatrically instead of reasonably, he falsifies heights (pretending a two-story building is not two stories), he sacrifices reason and convenience for the sake of romantic theatrical whims, etc., etc.

Of course no architect is perfect. But you have only to live with some of Jefferson's buildings a few years to notice their occasional shortcomings. And to love them the better for all that, as you might learn to love a turtle with three legs.

But the Pantheon, to get back to that "model" for the Rotunda.

I never could believe that Jefferson, for all his blunders as an architect, could not have turned out a Pantheon if he had really wanted to.

And nobody ever persuaded me that Jefferson was a "classical" sort of fellow with unbounded reverence for Greece and Rome.

The rights of man, revolutions, an overly developed taste for watching thunderstorms, a passion for all new mechanical gadgets and gewgaws -- that is not the classical mode.

The first day I noticed he had sawed a hole in the floor of his entrance hall for his clock weights to sink through, I knew he was my kind of man, and about as classical as a twisted ankle. Glorious, yes, but hardly classical.

It was odd, even for Jefferson, to take the noblest dome of the classical world and reduce it to doll-house size (relatively) and then start tampering with colors and pediment proportions, and so on and on.

And then I discovered the chapel of the Villa Maser, the last work of Andrea Palladio, and the last work of his life. It was built the year of Palladio's death in 1580 (250 years before Jefferson's Rotunda) and the two buildings are as like as two dolphins.

Now Desmond Guinness is an Irishman, a great authority on Palladio, and his book "Palladio: A Western Progress" traces the Palladian influence in a dozen countries including America.

His book also includes a picture of the chapel of the Villa Maser, and I lost no time when he was in town recently to ask him about it.

No, he said, Jefferson never saw Palladio's chapel, so startingly like his own Rotunda. Jefferson traveled in Italy, but never saw it. And although Jefferson corresponded with everybody and his cousin Ermintrude for 80 years, there is nothing to suggest Jefferson even heard of the domed chapel by the architect he practically worshipped.

Guinness pointed out that Jefferson called Palladio his "Bible" for architecture, and points out the domed chapel is one of his most disarming buildings -- you have to be a real clod not to fall in love with it -- and yet it is merely coincidence that the chapel and the Rotunda are so nearly the same building.

Ha. Which is more likely:

That Jefferson never heard of this final masterpiece of his favorite architecture, a building already 250 years old when Jefferson built the Rotunda.

That Jefferson scholars and architectural buffs have simply failed to uncover the documents that prove Jefferson knew this building, loved it, and modeled his own masterpiece upon it?

I met Guinness at the incredible F Street House of Virginia Bacon. It sits precariously at the edge of a goodsized abyss formed by tearing down neighboring houses and (evidently) setting off atom bombs in their basements.

But inside Bacon House the chandeliers still burned with candles, and the oak in the fireplace still burned 24 hours a day all winter, and Mrs. Bacon herself was in full regalia with her wit at full steam and all systems GO, from the basins of macadamia nuts to the ultimate ambience of the place. Old Lowestoft, old silver, and (as I caught myself in a mirror) old guests. Well, that cannot be helped.

So much the greater reason, as I said to myself at the time, to enjoy remarkable things as they occur. One may indeed be approaching middle age, but one does not suffer in Virginia Bacon's house, let me tell you.

The hostess was standing -- she uses a stick to support herself and reduce wear and tear on the legs -- because she likes to stand when she receives guests. She is not even 90, and people might think it rude if she sat while they stood. So there she was, up and at 'em.

I remarked on the huge portrait of her as a very small girl -- it was hanging on a wall 73 feet distant and was easy to see. I could not help noticing the baby girl looked astonishingly like the hostess, now a grande dame for nobody knows how many decades.

"I remember when he painted it," she said, on the verge of some tremendous laugh. She drew conspiratorially close. It has struck me that when Mrs. Bacon says something to you, you always have the impression she is going to spill the most astounding beans, because she gives full weight and attention to even the idlest comments of her guests.

"He told me to stand with one foot on top of the other -- said that would amuse me. Needless to say, it did not amuse me in the least. What would have amused me would have been for him to paint me while standing on his head. Now that would have amused me at the age of 3, but not standing with one foot on the other."

"And did he?" she was asked.

"No." She said it with the tone of one who well knows the baseless fabric of the vision. "He could not manage so much."

Which was the real Virginia Bacon, I reflected, the little girl the painter tried to amuse during the long hours of sitting for the portrait, or the grande dame in front of me now, with the experiences of a long life added to the child.

As a child she wanted the painter to stand on his head. I do not say she has progressed entirely beyond that wistful hope -- it might still amuse her -- but somewhere in the years since, a style has developed.

The candles -- listen, Mrs. Bacon is a pyromaniac -- have smudged the high walls of her drawing room. Her style is not to worry about candle smoke. Like Jefferson, who chopped the hole in the floor for the convenience of his clock.

Some things are important, some are not. The choices, endlessly chosen, make the style.

As with Jefferson and his Rotunda. People can say, if they wish, that he copied the Pantheon. If they really cannot see how totally different in effect the two buildings are -- as different as a baby and an elder statesman.

I say he knew the Villa Maser chapel and said to himself in a flash, "Now this is what I can do with the Pantheon."

But even if he never knew that chapel, his own style so transformed the Pantheon (as he somehow managed to transform everything else in his way) that to this day nobody can really say how much he owed to Palladio, or to Agrippa, or to Paris or to Rome.

But what you can say when you see Monticello or the Rotunda or any of his other toys, is that they delighted him more than any rattle in the world and are his in a way that only style -- not substance -- could confer.