Eleusis (card game)


Eleusis is a shedding-type card game where one player chooses a secret rule to determine which cards can be played on top of others, and the other players attempt to determine the rule using inductive logic.
The game was invented by Robert Abbott in 1956, and was first published by Martin Gardner in his Mathematical Games column in Scientific American magazine in June 1959. A revised version appeared in Gardner's July 1977 column.
Eleusis is sometimes considered an analogy to the problems of scientific method. It can be compared with the card game Mao, which also has secret rules that can be learned inductively. The games of Penultima and Zendo also feature players attempting to discover inductively a secret rule or rules thought of by a "Master" or "Spectators" who declare plays legal or illegal on the basis of the rules.
The formalization of Eleusis+Nobel inspired new modes of communication by exchange of logical notes.

Rules

The game is played by creating a row of cards in sequence. At the start of the game the dealer invents a secret constraint for how these cards must progress: for example, "each card played must be higher than the last, unless the last card was a face cards in which case any numeral card may be played".
Two decks of cards are shuffled and 14 cards dealt to each player except the dealer. One card is dealt face-up to start the row and a random player chosen to start.
On a player's turn they must add one or more cards from their hand to the row, in sequence. The dealer judges this play: if the entire play fits the dealer's rule, the cards are left in place as part of the row. If they are invalid, they are removed from the row and "sidelined" below the card that they attempted to follow, and the player is dealt a number of penalty cards equal to twice the number of cards they attempted to play that turn. If multiple cards were played this turn and only some were incorrect, the entire play is declared invalid, without the dealer specifying the invalid cards.
One player may be the "prophet". A player who believes they have worked out the rule may become the "prophet" at the end of their turn, if there is not already a prophet among the players, by placing a black marker on the card they just played. The prophet puts down their hand and skips their turns during their time as prophet. The prophet takes on the role of judging valid and invalid moves: if the dealer catches them making a mistake, the prophet is overthrown and receives five penalty cards. An overthrown prophet takes their hand back up, takes all black markers off the row, and becomes a regular player again.
If at any time a player thinks they cannot play a legitimate card, they may declare a "no play", and show their hand to everybody. If the dealer confirms that no cards in that hand can be played, the player discards the hand and draws a new hand four cards smaller. If the player's call was incorrect, the dealer plays the correct card for them and gives the player five penalty cards.
A white marker is placed on each tenth card played, and a black marker on each tenth card after a prophet's marker. After the fourth black or white marker is placed, any invalid plays result in that player being eliminated from the game.
The game ends when a player empties their hand, or when all players have been eliminated. Players score 1 point for each card in the hand of the player with most cards, minus the number of cards in their own hand. If a player has an empty hand they gain a further 4 points. If there is a prophet at the end of the game, they receive an additional 1 point for each card in the row following their first black marker, and 2 points for each sidelined card following that marker.

Eleusis Express

In 2006, John Golden developed a streamlined version of the game, intended to assist elementary school teachers in explaining the scientific method to students. It has the following differences:
Abbott himself considers the variant a "great game", and refers to it as "Eleusis Express".