Now, however, reality is everywhere you look, taking dizzyingly protean forms. For every blockbuster that conjures a brand-new, hermetically sealed cosmos of fantasy, there are at least a dozen movies chasing after that “fundamental rapport” in new and sometimes confusing ways: 2010 may be the year of the multiplying reality effect. We have seen outright hoaxes, possible hoaxes, movies in which real people play fictional versions of themselves, exercises in trompe l’oeil navel gazing and ruthless self-examination. Not to mention slickly packaged, meticulously detailed attempts to reconstruct the truth of history, occasionally by making it up more or less from scratch.

Take the movie everyone seemed to be talking about this fall. Is “The Social Network” accurate? Is it true? Do its polished surface and carefully engineered visual and sonic effects count as realism at all? Every commercial biopic invites this kind of scrutiny, and whenever a new one is released, someone publishes an article lining up the discrepancies between the historical record and the Hollywood version. Even before “The Social Network” was released, The New Yorker broke the news that Mark Zuckerberg (the real one, not the one played by Jesse Eisenberg) has had a steady girlfriend for most of the period covered in the film, a detail omitted from the movie, which makes much of its protagonist’s inability to sustain relationships, or even conversations, with women.

But the public surely knows — don’t we? do we? — that movies take liberties, and that the words “based on a true story” or “inspired by true events” appearing before the opening titles offer at best a loose and flimsy tether to reality. We are either sophisticated enough not to trust that what we see corresponds to what was, or jaded enough not to care. There may be an extra dose of cognitive dissonance when the biopic subject is, like Zuckerberg, still alive, not yet 30 and very much in the public eye. But surely we are used to that kind of feedback loop as well.

Other movies trod muddier ground, turning the question “Is it real?” into a kind of double dare. To ask the question is to risk seeming naïvely literal-minded; not to ask could make you a sucker. That, at least, was the trick attempted by Casey Affleck’s “I’m Still Here,” a multimedia publicity stunt wrapped around a transparently fake documentary. The subject of this carefully staged celebrity train wreck, Joaquin Phoenix, provoked much puzzlement with his infamously hairy and unhinged appearance on “The Late Show With David Letterman.” By the time he and Affleck revealed that the actor’s bizarre public behavior — rambling incoherently, growing a beard, announcing that he was forsaking acting for a career in hip-hop — was a put-on, and the movie a prank, pretty much everyone already knew and pretty much nobody cared. The attempt to make a point about the fungibility of identity in an age of shallow celebrity foundered because it was too obvious, too elementary. Pretending to be someone else, or a different version of yourself, in front of the cameras is no great feat or revelation. It’s a fairly normal mode of being, for the famous and the obscure.

And besides, the simple binary choice that Affleck and Phoenix offered viewers — earnest or ironic? hoax or not? — was much too unsophisticated. They were the ones who looked naïve for supposing that anyone would fall for their stunt. But “Catfish” and “Exit Through the Gift Shop,” two documentaries that premiered at Sundance in January, were more slippery. The credited director and, at least at first, the ostensible subject of “Exit” is Banksy, the artist whose conceptual graffiti are as recognizable as his face is unknown. But what begins as a tour of the world of international street art quickly becomes something else. A documentary about Banksy and his colleagues, directed by an amiable Los Angeles-based Frenchman named Thierry Guetta, turns into its opposite, as the would-be (and apparently incompetent) documentarian remakes himself into an art-world pseudo-celebrity known as Mr. Brainwash, whose rise to fame is dutifully recorded by Banksy himself.