Surely there are few groups with a greater willingness to suspend their disbelief than the people who play video games. Whether we're pretending to be commandos in follow-the-leader first-person firework displays like Call of Duty or a petal floating on the wind in a game like Flower, we're always on the front lines of make-believe.
At first glance, the BioShock series seems to demand a greater will than most. The original game took place in a city at the bottom of the ocean where you could inject yourself with a blue liquid that let you fire bees out of your hands. The latest one, BioShock Infinite, is about a flying metropolis called Columbia where people travel around by hooking onto a network of overhead rollercoasters.
Your job is to rescue an innocent girl who seems to be able to rip through time and space and is being pursued by a giant mechanical songbird. Oh yeah, and it's 1910.
So why, if you'll excuse the pun, doesn't it all fall down?
"The most important thing with any of these things is that you create a sense of consistency," says Ken Levine, the creative director of developer Irrational Games. "That you make a leap, but some of it is based on science."
The root of that consistency, in this case, is the one thing Levine won't really talk about. "The prime thing that happens in Columbia to set everything in motion is the thing that makes it float," he says. "And there is a scientific explanation. It's not something that would be possible today, but it's connected to everything that's going on in Columbia."
So we don't know what makes it float, but we do know why it was built. At the turn of the 20th century, America was at the peak of its national optimism. The previous few decades of innovation, discovery and expansion had made her strong, and Columbia was an emblem of that strength.
But it was also designed to export that strength, and following a violent international incident the floating city became a rogue state and disappeared.
You have found it again. Playing as a cynical former Pinkerton agent called Booker DeWitt who thinks he's seen everything, you're charged by a mysterious benefactor with rescuing a girl called Elizabeth. Imprisoned in a tower for 15 years, Elizabeth is practically your opposite - she's no fool, but she is innocent and naive and bursting to embrace the world you've given up on.
Together you try to escape, which is easier said than done, because half the population wants Elizabeth back in the tower and the other half wants her dead.
Like Irrational's other games, the path you tread is largely chosen for you, but the manner in which you tread is your own design. There are projectile weapons like pistols and shotguns to choose between, and also Vigors - special powers that let you lift enemies from the ground or attack them with flocks of angry birds. You can also direct Elizabeth to use her powers to assist, creating cover, escape routes and even allies to fight alongside you by dragging them into your reality through "Tears" in your surroundings.
One change here is to the way some of your passive abilities, called Nostrums - Infinite's equivalent of BioShock's gene tonics - are utilised.
"When we looked back on the first BioShock," says Levine, "one problem we thought it had was that people didn't feel wholly connected to the character because there wasn't permanence in the character-build system, and you could swap anything out at will."
So Nostrums are permanent. Some of them you encounter at specific points and all players are meant to gain them, but sometime you have a choice. When you find these "Pot Luck" boxes, you choose one of four Nostrums and it becomes a permanent part of your character.
"We want lots of those very granular choices," says Levine. "But they are permanent granular choices as to how your character evolves across the game."
Other seemingly benign or morally ambiguous decisions, like euthanizing a horse or rescuing a man you don't know from a lynching, will weigh on the outcomes too.
"Quite often the theme of our games relates to unintended consequences, and I think we see that where choices are made in this game you're not really sure what the consequences will be," says Levine.
"And there's no angel or devil - Elizabeth's not going to be the angel all the time saying, 'Do this Booker, do the right thing,' because both of them learn very quickly that there's not always a right thing."
Indeed, like Rapture before it, Columbia has been extrapolated from some of the most interesting fringes of the prevailing science and philosophy of its time, and it's the number of ways the people and situations of Columbia have marinated in those ideas that makes the backdrop to the player's story so interesting.
"There's a bifurcation that happens in the city," says Levine. "The original idea was that this city was going to be a floating symbol of the American ideals, of the founding principles. But as quite often happens with political movements, there are people who get different ideas about what that actually means."
The first person to get different ideas in this case is one Z. H. Comstock, who comes into power and takes a more extreme view of the American ideal, turning veneration of the Founding Fathers into a kind of worship. On Comstock's watch, Jefferson, Adams and Franklin graduate from symbols to gods.
In response to this, up rises a worker's movement called Vox Populi, led by a woman named Daisy Fitzroy, and initially the group offers reasonable alternatives. But as Vox Pop gathers followers and starts to threaten Comstock's Founders at a political level, the friction raises the temperature considerably.
"It's very much inspired by looking at groups like the Baader-Meinhof," says Levine, referring to the extreme left-wing group active in Germany between 1970 and the late nineties. "I remember an interview with someone who left the group who said, 'I started to protest Nazis in government and then found myself working with people who blew up an Israeli Airliner, and I don't know how I got there.'"
In one of the demos of the game we get to see, Fitzroy's image is projected onto a giant red banner and she rails against "the big boss" - her idea of The Man - and how he views the worker as an animal to be flogged to death then chopped up and eaten. In the foreground, her followers are preparing to execute a postman.
"Essentially what's going on is a form of ethnic cleansing," says Levine. "She's clearing out this part of the city, moving out the Founders and moving her people in, and anyone connected to the Founders - in this case a poor shmuck, a postman who doesn't know anything - is going to get caught up in it."
As in previous BioShock games, you will get to explore the motives and actions of ideologues like Comstock and Fitzroy by digging around the edges of the interactive space for tape recordings and visual records of their behaviour - like storefronts shut down and smeared in red paint declaring they have been taken back by the workers.
Infinite introduces another layer to this storytelling through its use of objects and other people in the world.
"You saw the guy getting beat up outside the store," Levine notes. "We have a system where the AI say to each other, 'Hey, I wanna beat someone up! Is anyone available to get beat up?' And another AI will say, 'Oh I'm available,' and this stuff happens dynamically. But if they're in combat or something else is occurring, that won't happen yet. We have this very opportunistic system that lets us create that kind of content if the opportunity arises."
Another part of that system relates to Elizabeth. Freed from her confinement, she is full of energy and excitement.
Elizabeth herself is different to the other clever things BioShock Infinite is doing.
BioShock has been fascinating so far for lots of reasons - for me the main one is that they explore interesting ideas under cover of entertainment - but while there has been much to admire and to ponder and to question, we have really loved the game as a whole rather than an individual within it.
More on BioShock Infinite
Also this week: Payday 2 and BioShock Infinite's Rapture DLC.
The first DLC is a wave-based combat game - and it's out today.
Latest Heavy Hitter enemy revealed.
In Elizabeth, and in her childlike joy and enthusiasm that's painted so vividly against the jaded backdrop of Booker's bleaker worldview, BioShock now has a heart to go with its brain.
"One of the joys is watching Elizabeth discover herself, because she has no idea who she is," says Levine. "I think watching her discovery is fascinating and watching her powers is fascinating."
Still, it wouldn't be very interesting if you were forced to sit and watch her discover herself. It has to seem spontaneous. To this end, the internal game logic has a schedule of incidental things Elizabeth can do in the world that develop her character and her relationship with Booker.
We see her put on a Lincoln hat and playfully start reciting the Gettysburg Address, for instance, but you don't have to see that happen in that one spot - if you're doing something else in the room, it can happen when she finds another hat later. And the game knows to ration those events across a level, too, rather than jamming them all into one sequence or doing them at an inappropriate time.
It's all part of the same internal consistency that makes it easy for us to make-believe that a city can fly. It's still a willing suspension of disbelief, but it's much easier to summon the will in environments so rich with forethought as those you visit in BioShock Infinite.