Nantucket or Martha's Vineyard? How about both?

They're a natural extension of life if you grew up in Boston or wherever Red Sox caps are ubiquitous and if Cape Cod is too bourgeois.

Nantucket and Martha's Vineyard. The very names, for many of us from other places, conjure thoughts of lobsters and clams and harpooners and presidential getaways and weathered houses facing the salty sea and solitary walks on beaches and — at least with Nantucket — limericks.

A gentleman came to Nantucket

With nil but a shovel and bucket ...

But — aside from both being gorgeous and islands we'd all love to spend summers on if we could — what are these places, really? How is Nantucket different from Martha's Vineyard? Is there actually a vineyard on Martha's Vineyard? (Hint: There isn't.) Can you afford a weathered house facing the salty sea on Nantucket? (Hint: Got a few million in the trust fund?)

They're both Massachusetts islands south of Cape Cod — not too far, but Nantucket more distant — and reachable by ferries and other watercraft, or little airplanes.

Nantucket: An island with one town — simply "Town" to locals — full of perfectly groomed houses pleasant to look at (the whole island is a National Historic Landmark District), fresh seafood and enough places to spend a night or three or a season. The island is basically flat, aside from bluffs overlooking the sea, a sea that's menacing some of those bluffs and forcing homeowners to move their houses back a bit, lest they tumble into worthlessness. Great bike trails. Good beaches.

And Martha's Vineyard co-starred with Roy Scheider and a fake shark in "Jaws." The association is a tired cliché — the movie is 42 years old, people — but shops there still peddle "Amity Island" signs, so ...

"This bridge coming up is affectionately known as the 'Jaws Bridge,' " said Nancy Gardella, of the chamber of commerce, during a drive-around. If you've seen the movie, you know the bridge. "And despite the fact that there's a 'Keep off the bridge, no jumping or diving' sign, typically in summer, the bridge is lined with kids who stand along the edge and jump off."

Which is a reminder: Both islands are fine for kids.

And both share a nautical, grassy-duned, artsy-literary and just-painted sensibility. Each summer, the population of these islands routinely jumps from a combined 25,000 or so to five or six times that, and it's not just the beaches.

What's kind of curious is that despite their proximity — about 70 minutes apart by high-speed ferry — islanders tend to stick to their own turf. Dick Burns is a bookseller at Mitchell's Book Corner in Nantucket town. "We've got Nantucket," he explained. "I've spent, literally, about six hours on the Vineyard." He's lived on Nantucket since 1972.

The closest thing to Nantucket town on the Vineyard is Edgartown. Like Nantucket, it's a village of Cape Cod-ish and colonial houses that beg to be photographed. As with its cousin, it has restaurants (some high-end), shopping and galleries. The Old Whaling Church (1843) is a whale of a church that doubles as a concert venue and makes a nice counterpoint to Nantucket's newer Whaling Museum; smaller St. Andrews Episcopal Church (1899) boasts two stained-glass windows autographed by Louis Tiffany.

A 15-minute walk from the center, on its own beach, is Edgartown Lighthouse, one of five on the island (Nantucket has three) — and on this day, Walt Looney was releasing a slightly undersized striped bass he'd just coaxed to the sand.

"I was hoping to catch a bluefish for dinner," said Looney, a lawyer who's been coming to the Vineyard for 25 years. "I live here now. I haven't been to Nantucket in a long, long time."

As for the island's two other towns and three smaller ones, each is a little different from the others — which makes them worth poking around.

There's no denying Nantucket's cobblestone charm. There's also no denying Nantucket's corporate pedigree. Writers (William Styron, Lillian Hellman, more) and celebrities (Jackie Kennedy Onassis, John Belushi, more) are or were drawn to the Vineyard and its famously tolerant villages, but the serious money (Jack Welch, the Heinzes, more) has tended toward Nantucket and its $10 million shanties.

"The red roof through the trees there? John and Barbara Hersey. Friends of my parents," he began. For a time he'd been a taxi driver. "I drove Mike Wallace. And I drove the late Beverly Sills. Her friend from San Miguel de Allende was my mother's college roommate."

I asked, inevitably, about the impact on the island of "Jaws."

"I'm in there," he said. "Guitarist, in the opening scene."

Yep, he's in there: 14 seconds on guitar, near the bonfire, billed as Mike Haydn, his hair not yet gray .

There was a guitarist named Haydn

Oh: The fishing is excellent off both islands. And if you insist, on either island you can charter a bigger boat.