I am not suggesting that all game rules are a deliberate form of artistic expression. Backgammon, for example, is an old and a great game, but its rules have no obvious meaning beyond being a fun gambling game, possibly derived from Mancala. However, I do claim that the creation of a set of rules within which the successful player must be creative is a form of expression exclusive to the domain of game design. No other art form does this.
Rules in Context
Let's examine some systems to see how rules have been designed so far. Here, we shall divide games into types, according to where the rules are created and where they reside during gameplay.
Type 1: Rules are created in advance by a game designer (person or team), and there are few enough that they can be held in the player's mind during game play.
This class includes most family board games. In the digital age, we'll call simple or action computer games Type 1a. (We'll get to "a" subsets in a bit.)
Type 2: Rules are created by a game designer and held in a book or umpire during play, with limited rules being held by the player's mind at any one time.
This type includes more complicated cardboard war games. Computer adventure games would be Type 2a.
Type 3: Rules are created by a game designer in advance, and as it is played, extra rules are created or changed by an umpire or player.
This type includes pen and paper roleplaying games, as well as professional military umpired war games.
Type 4: Rules are created at the start of the game by the player or umpire and modified as it is played.
This type includes children's play or make believe.
With the exception of Type 4, the designer's selection and creation of rules in advance sets the framework for the entire game. In Type 4 games, the designer is creating rules freeform to suit the situation and audience; this can become a team activity with several players becoming the game designers.
Rules and Machines
What is the relationship between these rule contexts and computing machines?
For types 1 and 2, there are computer (artificial) equivalents as noted in the examples. I have called them Types 1a and 2a.
As you can see, there are no 3a and 4a examples, because they do not exist yet. Type 4a would have the rules created at the start of the game and modified by an artificial player or artificial umpire.
If we could design computer contexts for Types 3 and 4, how would they behave? What would the player experience? Would they be capable of expressing a meaningful message?
One can imagine a Type 3a game that inherits from pen and paper roleplaying games or umpired war games. The players would be motivated to do things "beyond the rules" - and an artificial umpire would generate new rules in response to this desire, in real-time. We can call this a "judgment system."
For example: "I want to commandeer those civilian vehicles and use them to transport my infantry section to the next town, ahead of the main battalion." The umpire then decides the chance of this scheme's success, which is not covered in the rules.