It has now become routine to promote a new videogame by trumpeting the virtues of its “realistic” AI. But the notion of “realistic AI” at best covers a multitude of sins, and at worst is a contradiction in terms. Apart from the rare games that try to create learning intelligences within the gameworld, such as Black & White, the term AI is often used as a kind of shorthand for what is really something else entirely. This column is not about true AI but about unmasking the impostors.

We all know that if many games had anything like “realistic” AI they would be completely unplayable. Despite the amusing precedent set by the portly Steven Seagal in his naval-themed action movies, a single soldier has less than a squirrel’s chance on Mount Etna of successfully storming a military vessel. To judge by his limited punch/punch/spin-kick/strangle repertoire of barehand combat, Solid Snake doesn’t even know aikido. Hence the “AI” in Metal Gear Solid 2 actually takes the form of generous lashings of dumbness. Understandably, a guard will become suspicious on seeing a wet cardboard box in an interior corridor; on the other hand, if you get seen and then evade long enough, the guards will eventually forget they ever saw you, rather than initiate a permanent vessel-wide alert until they hunt you down and shoot your face off.

It helps that the guards are so ocularly challenged, being cursed with a combination of tunnel vision and acute myopia. But it would be trivially easy for a developer to give his enemies 20/20 vision, military-standard marksmanship, ruthless perseverance, and a penchant for team flanking strategies that would mean game over every time. So this species of “AI” is actually a deliberate ramping down of the enemies’ optimal intelligence. It’s artificial stupidity, and the developer chooses the right level of dumbness to make the game a reasonable challenge.

Artificial stupidity is the rule in beat-’em-ups, too: Soul Calibur would be unplayable if your opponent blocked all your blows with perfect green parries every time and then unleashed swingeing 10-hit combos. The developers must put chinks in their defensive armour, and leave the player to discover how to exploit them. Pretty much all action games partake of AS in one way or another – even the supposedly “realistic” FPS products such as Counterstrike, with its accurately modelled recoil and proper guns. In the finely tuned stupidity of its enemies, Counterstrike is no more realistic than the joyously deranged scarf-controlled rubber-world sim Freak Out.

AI can also be suffer from the dreaded evil of incoherence – that moment when you realise the game isn’t actually playing by its own rules. In Red Faction, there are some nods towards believable AI – in the sections where, disguised as a scientist or businessman, you learn to evade detection by keeping your head down and not looking directly at any of the guards. While this isn’t actually “realistic” – because it’s not necessary for someone to look at you before you recognise them – it’s a logical simplification. But Red Faction becomes incoherent when you discover that the guards apparently have a sixth sense for weapons. At a distance where they wouldn’t normally see you at all, you only have to pull out a gun to be mobbed by the enemy. This sits ill with the rest of the enemy behaviour and is a rule that you work around sulkily, rather than one whose challenging strictures you actually enjoy.

Game AI can also feel incoherent in a different way when it appears that you are operating under different rules from those of your competitors. While it is arithmetically necessary for the player to be given deadlier abilities than the enemies in a one-against-many killfest, it becomes annoying when the situation is reversed in a straight test of skills – as seems endemic in the racing genre. In Metropolis Street Racer, you are racing for kudos and skill points, and so you get penalised for collisions with other cars. But the other cars mercilessly ram you from behind at every opportunity. They don’t worry about losing points at all: for them, it appears to be a straight, aggressive race to the finish. So in effect, there are two different races happening on the same track, and yours is harder.

In Gran Turismo 3, if you’re powersliding round a bend and an enemy car clips your rear, you spin out. Fine: that’s what would happen in real life. (In real life, cars don’t stick madly to the racing line at top speed no matter what’s in front of them: they tend to want to avoid collisions. Still, okay, it’s a bumper-car sim.) But however hard you ram the other cars from behind, they will never, ever spin. They’ll just give an insouciant little waggle of the back end and then speed off into the distance. You’re often driving a more powerful car to compensate, and the enemy drivers are made artificially stupid by braking earlier than they need to round every corner. So the rules are levelled out, but asymmetrically: in a way that, finally, feels like a bit of a cheat.

The result of the industry-wide abuse of the buzzword “AI” is to make games that are marketed in this way all the more disappointing when we discover their inconsistencies. There are still limitations, of course, even in the astonishing leaps made in “true AI” games such as Black & White. You cannot teach your tiger to play chess. But while Molyneux continues to refine his neural algorithms, the next fad in AI mechanics at least holds out the promise of greater coherence in the fantasy.

The useful thing about the flocking behaviour of small animals, as featured in the upcoming Herdy Gerdy and Pikmin, is that it is relatively computationally cheap compared to modelling human behaviour, but its rewards in believablity are great. (With a ZX Spectrum and the right rules, I discovered in my mis-spent youth, you can give a pretty good impression of a handful of birds flocking slowly around the screen.) And until the day arrives in the sci-fi future when you can have a convincing natural-language conversation with an NPC, all we ask for is a coherent illusion of life inside the machine.