Movies, as a rule, are not particularly introspective about the building blocks of romantic relationships. And if that's true of movies as a rule, when it comes to romantic comedies, that rule has pretty much been carved into stone by lightning and carried down a mountain by a guy with a long white beard.

(500) Days of Summer is the kind of independent comedy that, at first glance, might seem like it's going to be insufferable. Director Marc Webb -- a music-video guy better known for working with 3 Doors Down than with a feature film script -- trots out more than a few visual quirks. The very premise -- following the arc of a relationship out of chronological order -- seems fraught with gimmicky dangers. But no matter how goofy the film gets at individual moments, it becomes fairly irresistible for one simple reason. When it comes to understanding heartbreak and the role of different loves in our lives, it's almost painfully wise.

Joseph Gordon-Levitt stars as Tom, a romantic soul working at writing platitudes for a Los Angeles greeting-card company, despite education as an architect that he's putting to no use. Into his life steps his boss' new assistant, Summer (Zooey Deschanel), inspiring an instant infatuation. She's cute! She digs The Smiths! She's the kind of girl with whom you can make a delightful day just strolling through an IKEA store! So what if she claims she doesn't believe in love?

The opening narration makes it clear that our two lovebirds will not have a happily-ever-after; the on-screen counter flips to the day of Tom and Summer's breakup before we even have time to think of them as a couple. And while swinging back and forth in time between their happy couplehood and Tom's despair might have come off as an unnecessary contrivance, breaking the story into discrete pieces allows Webb and screenwriters Scott Neustadter and Michael H. Weber to build a thematic framework: the notion that most people retrospectively think of their relationships in those bits and pieces, rather than the larger story they tell.

And many of those bits and pieces are simply glorious. One hilarious montage finds a blissed-out Tom flitting around the office, solving every creative block with a pithy heart-felt sentiment; another sequence turns the morning after Tom and Summer's first sexual encounter into a fully-choreographed production number set to Hall & Oates' "You Make My Dreams," complete with animated birds and a marching band. And if you're not won over at the outset by the brilliantly bitter opening "disclaimer," you're a hard audience to please.

But as charming as (500) Days of Summer may be when it's funny, it's even better when it's poignant. Joseph Gordon-Levitt continues to prove himself as a young actor with an impressive range, and he's wonderful as a guy immersed in every emotional moment. Deschanel might actually have an even tougher challenge, as she has to she has to sell Summer's commitment issues as genuine without turning her into an ice queen. Together, they find a perfect pitch for two achingly wonderful late scenes: the wedding of a mutual friend at which they re-connect after their breakup; and a party that splits the screen between an outcome Tom hopes for, and what actually transpires.

It's in these moments -- and in several that surround it, as Tom tries to make sense of what went wrong with Summer -- that (500) Days of Summer turns damn-near profound. Most romantic comedies deal with the wacky complications of winding up with The One; this one takes on the tougher task of understanding The One That Got Away. There's a relationship that teaches you what you have to know before The One ever has a chance of being The One, and that's what the filmmakers here understand: Lasting romantic happiness probably never comes without first surviving a few deep battle scars.

It's a bit of a shame that Webb and company overplay their quirky hand at times. They give Tom a wise-beyond-her-years pre-teen sister (Chloe Moretz) as his guru and confidant, complete with utterly implausible dialogue. Indeed, most of the supporting characters are exactly the kind of types -- the jerky best friend (Geoffrey Arend), the vaguely oblivious boss (Clark Gregg) -- that you'd find in a much lazier romantic comedy. (500) Days of Summer manages to be both uproarious and wistful by doing what those other romantic comedies so rarely do: telling the truth.

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(500) DAYS OF SUMMER

***1/2 (three and a half out of four stars)

Starring: Joseph Gordon-Levitt, Zooey Deschanel, Geoffrey Arend.

Directed by Marc Webb.

Rated PG-13