Prophet

"Prophet" (our term for it, which is more pronouncable than the original name "Eleusis") is a card game invented by Robert Abbott. As Robert makes a living selling games and rules, and it has been described several times in print and and on the web (see below), I won't repeat the rules in full here. However a brief description is in order ...

The object of the game is to find out the rules.

Players take turns setting the rules of the game (acting as "God"), secretly determining which cards can be played after each other. For example, "God" may decide that red cards can only be played after black cards and vice versa. The players take turns laying down cards. If the the card they play is correct under the secret rules, "God" allows them to go again. If not, the next player takes their turn trying to play the right card. Furthermore, when a player believes they have deduced the rules of the game, they may declare themselves to be the "Prophet". From this point, they speak for "God", telling players whether they have played correctly or not. Of course, should they interpret wrongly, they fall from grace and cease being the prophet ...

Each player takes a turn as "God". Points are scoring for playing correct cards, and (when one is "Prophet") for correcting interpreting the rules. Crucially, "God" scores points based on the difference between the highest and lowest score in the round they set the rules.

It's this last point that is the important one. It's in "God"'s interest to make rules that will produce the maximum separation in players scores, neither hard nor easy but subtle. If the rules are too ornate, no one will ever guess them, all the players moves will be essentially random and the scores low and similar. If the rules are obvious, they will be guessed early, and everyone will score near maximum.

A suggestion then is to make rules that have exceptions or circumstances that reverse the normal order. For example: red cards can only be played after black cards and vice versa, except for aces which can be played anytime and royal cards which must be played after red cards. Beware of making rules based on even slightly obscure properties. If it involves primes or fibonacci sequences, forget it. I would also suggest avoiding rules that use a history or memory of more than one card. (That is, the correct card can only be discerned by examining the last two or more cards played.) This leaves the start of the game in an uncertain state (what's the zeroth card played?) and threatens to become too complicated.

Be sure your rule set is complete and unambiguous. Consider if there is a rule for what card follows any other card. Ask if any of the rules contradict each other, and if necessary establish precedence.

References

• R Wayne Schmittberger, New Rules For Old Games
• Robert Abbott's website and incomplete rules
• Ulrich Roth gives the rules, including a basic version. (He also suggests playing with a special custom deck, but to me that takes away something good about the original game - the simplicity of