So, basically, 'play' has been defined by those who take it seriously as a mentality, an attitude, a demeanor that melds certain aims (i.e. I want to be cheerful) with certain traits (i.e. being funny) and certain outcomes (i.e. increase in positive affect).

I would add a few things to this notion of 'play.' Playfulness can only take place in certain contexts. If serious stakes are involved—say a real-life battle between two warring groups—then a playful demeanor would likely be dangerous and maladaptive, at least in outcome. Also, playfulness is a process that can be done well or poorly, just like anything else. As the adage goes, it's not whether you win or lose but how you play the game. And if you play it mindfully—fully engaged, with the right balance of spontaneity and effort (though it may feel effortless) and well-practiced, well-sharpened skills—then you are playing at a high level. Think getting 'into the zone' in sports. The antithesis would be mindless play in which there is little energy, emotional investment and regard for the rules and outcomes.

The recently-released Sherlock Holmes: The Game of Shadows is a movie whose primary strength is that it provides a strong sense of play.

I should mention that as a movie the Sherlock Holmes sequel misses the mark in a few significant ways. For instance, the film fails to provide the intellectual stimulation of a twist-filled plot and razor-sharp protagonist that we would expect from the Arthur Conan Doyle series. The attention-to-detail and connecting-the-dots process inherent in advanced detecting and reasoning abilities would've been engaging to behold, but such ideas unfortunately take a backseat to witty banter and prolonged action sequences.

But overshadowing this flaw is a tremendously engaging sense of play. There are two main avenues the film takes in this vein.

First and foremost, Sherlock Holmes is a character that has unintentionally been molded to be a prototype of playfulness. He's playing even when he's serious. The unparalleled acting chops of Robert Downey Jr. is primarily channeled to exude his character with all of the personality qualities in the Bartlett definition mentioned above, from unpredictability to humorousness. Further, he doesn't simply detect crimes and pursue villains; he seeks to reframe all that is happening in a playful manner. For instance, when he's worked out the conspiracy involving the evil Moriarty (something he does in his mind relatively early in the film), he doesn't simply lay out his plan to his trusted sidekick Watson or to us as the audience. Instead, he dictates that the rules and steps to his plan leak out in as suspenseful intriguing 'need-to-know' manner, which he delivers with a showman's sense of dramatic timing. His sense of play is further highlighted by his tendency to rotate costumes as often as he re-packs his pipe, and to engage in such traditional adult play as drinking, dancing and chess.

Holmes reminds us of some other qualities of play. Play can be a solitary activity (Holmes is essentially a loner, and play is how he connects himself to the world), and play can also be a bridge of connection to others. Sherlock-Downey Jr. uses playful banter and the reframe of the Moriarty mystery as a game in order to re-connect with Watson - his best friend who is physically and symbolically drifting away from him through marriage to his new wife.

Also, in the same way that attention, engagement and creativity enter the equation in advanced stages of play—like when you've played a video game for ten days straight and you start to discover secret 'cheat' strategies—Holmes is constantly experimenting with various theories and substances in an effort to 'play' even more effectively. A prime example is when he spends his free time sniffing odd, rare chemicals (early in the film) and later, uses that knowledge base to detect the same smell in a more threatening situation. Such subtle environmental clues aid him in seeing the big-picture of what is being plotted by the villainous Moriarty.

The second way in which the film expresses playfulness is through the filmmaker, Guy Ritchie. Ritchie develops 'play' as a sensibility within the film, establishing such a relationship between the film and audience. For one, the notion of 'game' is everywhere, from the title, to an inordinate amount of references by the characters to such subtle priming as when he intersperses fight scenes with party scenes (early in the film there's a prolonged montage of Holmes fighting off assassins while darting through the crowd at Watson's bachelor party). And speaking of the action sequences and fight scenes, Ritchie clearly gives himself a timeout here to take a particularly playful approach—using slow-motion, multiple-layered soundtracks and inner monologue narration to punctuate these plot-irrelevant moments.

Movies often serve as a welcomed escape from harsh reality. Sherlock Holmes goes the extra mile in creating a playful atmosphere, serving to provide this 'vacation' function with uncommon effectiveness.