As a young architecture student, Craig Whitaker took some time off from study one day to go see a movie, a western. A spaghetti western, as it turned out, directed by the Italian Sergio Leone in Spain and starring Clint Eastwood.

Mr. Whitaker didn’t know that when he went in, but as soon as he saw Clint Eastwood ride into town, he knew the movie had not been shot in America, for Eastwood was riding into a plaza.

“In America,” he said, “We don’t have plazas. We have Main street.”

And there is a big difference between the two, which he suggests is deeply rooted in the culture. People pool in Plazas; they flow through Main Streets.

The traditional European town model, as replicated by Mr. Leone’s set designers, contains the people, surrounds them with the edifices of power, ecclesiastical or civic. In the traditional American model, people are encouraged to keep on moving.

“In Europe, you go down the aisle, get to the altar and go up to God. When you went to Versailles, there was the king’s bedroom right in front of you. There was no doubt who was the subject and who was the king. You bowed before Louis.

“Here we don’t want any of that stuff, we must be unimpeded. Even the Capitol in Washington is not set dead at the end of anything. It’s at an angle. You can bounce off and keep going.”

He grabbed a couple of cultural references: Willie Nelson On the Road Again, Robert Frost on The Road Not Taken.

“These are American ideas,” he said. “People can keep moving. Be born again. You can get up after having been thrown off your horse and go again.”

The idea of flow, it must be said, came as a bit of a surprise, when I asked Mr. Whitaker what made a good Main street. I had been thinking in terms of a post office, or church, or town hall, or maybe a village green or the architecture.

And the answer is it can be many of those things, or none of them, so long as the street is alive with movement.

There is a qualification to this idea of movement, of course. A good main street allows people to move through, but not to race through. It encourages them to linger, to interact in passing.

“Main street is a place to course back and forth, not to congregate,” he said.

There must also be what Mr. Whitaker calls “holes” to allow eddies in the flow, to offer what he refers to in his book Architecture and the American Dream as “gathering spots . . . offering a respite in the midst of surrounding buildings, all pushed out to the sidewalk.”

And these are some of the reasons he considers the main street in his town, Vineyard Haven, to be the best on Martha’s Vineyard.

He makes a pretty strong case for it.

“It’s got a Newel post at one end: the Mansion House. It’s the biggest building on the street and it’s at exactly the right spot. Like the head of the stairs.

“Main Street bends, so it’s got what architects call a closed perspective. It dips to the center and then rises again. William Styron said it has a rhythm of holes. The first is where the ice cream store is, the pizza place on the left. [Next comes] the Bowl and Board, and there is a hole for the Linden Tree, which is now gone.”

And, importantly, the commercial center ends, neatly, up past Le Grenier.

“The next building, a house, steps back and it says clearly that it’s the end of the commercial part of the street. So you know where the beginning and the end is.”

One might add that Vineyard Haven has a couple of other things going for it near Main street, if not actually on it. The supermarket and post office are an easy walk away.

One thing which Vineyard Haven decidedly does not have is distinguished architecture.

“There’s not one really great building on the street,” said Mr. Whitaker, whose architecture and urban planning firm is based in Manhattan. His book makes the point that Oak Bluffs, with its strong carpenter gothic motif, and Edgartown, with its white clapboard Greek revival buildings, are far more stylistically cohesive than the “Queen Anne/Colonial revival/mock Tudor/modern Cape Cod/California strip commercial” melange of Vineyard Haven.

The book quotes the famous author and Vineyard Haven resident William Styron: “Main Street will never win a contest for beauty or charm . . . the ugly duckling gains a place in ones heart by way of an appeal that is not immediately demonstrable.”

Except in Mr. Whitaker’s terms. So, let’s apply them to the other Island towns, and maybe see why their main streets work to varying degrees.

Circuit avenue, in Oak Bluffs, probably has the next highest percentage of plus factors. It has a clear beginning, although not one so declarative as the Mansion House. It also has, at its very center, a hole — the post office square, more properly the David M. Healey Square, as a gathering focus. Importantly, Circuit avenue flows right through and it is semi-closed at the other end, where the road bends. But instead of dipping, it rises in the middle, and the commercial district, as Mr. Whitaker notes, “sort of dribbles off around the corner.”

But isn’t it interesting that Oak Bluffs is the second most year-round place?

Main street Edgartown, in contrast — beautiful, architecturally-superb Edgartown — is as dead as a doorknob when the tourists are not in. All right, I exaggerate a bit, but only a bit.

It’s hard not to see this as a function of the fact that Main street does not flow anywhere. In ends at the harbor, in a parking lot with a wonderful view. The town badly needs a better finale to the street than a plaza for cars.

In the off season, life is elsewhere in Edgartown, nearly a mile away, up by the Stop & Shop and the post office and the Triangle shops. But where do the people go to course back and forth? In which bituminous car park?

And then there is West Tisbury.

“In the new West Tisbury business district, the buildings look like they’ve been dropped from an airplane,” Mr. Whitaker said.

“Cronig’s, the post office, the fire department are all set back from the road. You get no sense of what would make a Main street, which is buildings which front the street, which make you slow, make you feel you’re coming to a place. In West Tisbury, you’re not coming to anywhere.”

And who could argue? The cars blow past it at 30 miles an hour, and usually more. There is negligible pedestrian life.

The old center of West Tisbury, up the road a piece, with Alley’s and the Field Gallery and the old town hall and the Congregational Church, is a whole different thing. But the mass of the town has unwisely been taken elsewhere.

And perhaps that is the saddest town of all, for it could so easily have been so much more.

But we should still be grateful for what we have; for Vineyard Haven, Oak Bluffs, for what still remains in the other towns, for we still are doing much better than most places.

Main streets, as Mr. Whitaker notes, are in crisis all over America.

The new imperatives of commerce, the pull of the Wal-Marts and Targets, pull people elsewhere, leaving behind the little hardware store that’s going broke, the tiny drug store that’s locally owned, that also is going broke.

“What is wonderful on the Vineyard,” said Mr. Whitaker, “is we have been able to fill these vacancies. What we should be happy for is having a street people want to course up and down.”