Is Tetris allowed to be copyrighted?

(via Boing Boing) A recent court ruling says yes, but the reason that there was a real case at all highlights one of the basic issues intrinsic to legislating around art.

Copyright doesn't apply to sets of rules, only to the specific expression of those rules.  So iPhone developer Xio Interactive was able to argue in court that everything about Tetris constitutes a rule, rather than an expression.  A New Jersey circuit court ruled against them, but I want to take a closer look at the issue.

Ars Technica summarizes the case itself, and it's an interesting read.  In it, they quote the judge's definition of Tetris's basic ruleset, in order to work out what details beyond that point qualify as expression:

Tetris is a puzzle game where a user manipulates pieces composed of square blocks, each made into a different geometric shape, that fall from the top of the game board to the bottom where the pieces accumulate. The user is given a new piece after the current one reaches the bottom of the available game space. While a piece is falling, the user rotates it in order to fit it in with the accumulated pieces. The object of the puzzle is to fill all spaces along a horizontal line. If that is accomplished, the line is erased, points are earned, and more of the game board is available for play. But if the pieces accumulate and reach the top of the screen, then the game is over. These then are the general, abstract ideas underlying Tetris and cannot be protected by copyright nor can expressive elements that are inseparable from them.

It sounds to me like there should be more that constitute intrinsic rules to Tetris -- like the fact that the blocks are all possible combinations of 4 squares arranged so that their sides are touching -- but that's beside the point.  There isn't a Platonic definition of Tetris.

This is normal in a legal system.  It's one of the reasons we have courts and legislators -- to work out the sticky details between what's legal and what isn't.  And I think it's important to take note when the legal status of the work is in this way ambiguous.  Copyright obviously isn't well-equipped to deal with video games and electronic media, and it's being used ad hoc to compensate for that problem.  But as the world the law refers to changes, so must the law.