To what extent is it meaningful to talk about one game plagiarising another? All games draw upon structures and mechanics that exist prior to their creation, and indeed must do so in order to be comprehensible to their audience. So what are the boundaries for theft of ideas in a medium that is necessarily derivative? In order to explore this issue, let us consider one particular case study: the popular puzzle-slash-cRPG game Puzzle Quest: Challenge of the Warlords, which uses as its central element the "match 3 jewels" mechanic from PopCap's hugely successful game Bejeweled. Is this a case of plagiarism?
Firstly, I don't think there is any doubt that Infinite Interactive had seen Bejeweled before creating their Puzzle Quest game, and any innovation that can be assigned to the latter game can only be construed to originate in stealing the mechanics of Bejeweled and wedding them to a typical computer role-playing game structure. This may not seem very original, yet in videogames this kind of cross-pollination of genre elements can and is a source of originality. Puzzle Quest's design may rest upon pre-existing mechanics and structures, but the developers still made the decision to cross breed these elements, and having done so had to adapt and expand the mechanics of Bejeweled in order for them to fit into the new context. Since they did a good job in the process, to accuse them of plagiarism seems churlish and unfair.
For some time, accusations were leveled at PopCap that Bejeweled owed a debt to Nintendo's Tetris Attack videogame, which pre-dated it and is one of the first instances of a "match 3" mechanic - perhaps the very first. Yet here, claims of plagiarism would be wildly off-base. Not only is it unclear that PopCap had seen Tetris Attack, even if they had the earlier game displays none of the traits that make the later game so successful. The genius of PopCap in making Bejeweled was to create a game that could be played by anyone without any implicit stress (although a timed mode was also included for players who needed the additional excitement). This was one of the major design innovations of the last decade - a game so far from the gamer hobbyist's ideal of excitement and challenge that truly anyone could play it. Tetris Attack had none of this aspect to it - it was a conventional puzzle game, hitting all the emotional triggers of a conventional videogame. It had not innovated in the manner that Bejeweled had.
That Bejeweled is often copied is the surest sign of its success, and most of the games that copy it are strict cases of plagiarism. Goober's Lab, Sutek's Tomb and Zoo Keeper are all essentially the same game as Bejeweled, a theft of ideas that is not the basis for a lawsuit since game mechanics are not a form of intellectual property that can be protected. This is just as well - imagine how stagnant the first person shooter genre would be had (say) id Software owned a patent on the mechanics. We should be grateful that the kind of IP battles that hamstring creativity in other media do not apply to game mechanics.
Returning to Puzzle Quest, another point is worth noting: its cRPG mechanics are far more derivative than the workings of its "match 3" game, yet these aspects do not raise an eyebrow. Why? Because as a well-established videogame genre, cRPGs have already hurdled the plagiarism barrier. Once early videogames such as Ultima and Wizardry had successfully copied the major elements of the Dungeons & Dragons tabletop role-playing game in the early 1980s (itself owing a vast debt to tabletop wargames of the 1970s), the genre was established in its form. Now, new cRPGs may refine the details of the mechanics of these games in various ways, but few if any can claim to innovate in any major sense.
The fact of the matter is, game genres by their very nature become established because games borrow mechanics, structural elements, and conventions from earlier games. To have a videogame genre is to recognise a recurrent pattern of plagiarism that draws upon the successes of earlier games as its bedrock. This is a good thing for players: few but the most grizzled gamer hobbyists can face learning entirely original game rules every time they play, most prefer to play something that (in broad strokes, at least) strongly resembles an earlier game they have enjoyed. It means they have less to learn, and it increases the chance that they will enjoy the later game.
I work hard to come up with original mechanics for my videogames, but in doing so I risk creating a barrier between the audience and the games. Ghost Master, for instance, was highly original - but many players, trying to play it as if it were a strategy game, failed to get into what was innovative and interesting about the gameplay. My attempts to innovate had hurt the game. Similarly, Play with Fire leaves many players utterly confused as to what the play is supposed to entail (in part because of the unfortunate absence of a tutorial) because setting fire to blocks is far from an established game mechanic. With Reluctant Hero, my current cRPG project, I am attempting to walk a fine line - to innovate in the game structure and mechanics, but to do so in a way familiar enough to players that they can at least understand how the game will work. (The original PC version of this project has, alas, been suspended, but I have high hopes of resurrecting the project later this year in a new form).
It is the natural order of the videogame medium that games draw on earlier games within their genre (and from further afield!) Some games innovate, and in doing so they can attract new fans and devotees - provided the game is sufficiently familiar to spread to a wider audience. Some games innovate, but are so alien that they cannot hope to reach a wide audience. What would be considered plagiarism in other media is the backbone and lifeblood of the videogame industry, a well established system of building games from the ever-expanding toolkit of structural and mechanical devices that are the collective product of many generations of game developers. No-one owns these disparate ideas - and for this, on the whole, I suspect we should be truly thankful.