is a game
of inductive logic
, played on a chess
board. It was invented by Michael Greene and Adam Chalcraft in Cambridge
. The game is derived from the chess variant Ultima
(otherwise known as Baroque chess
), and played with a standard chess board and pieces, each piece having different movement and capture rules from standard chess. In a manner similar to the game Mao
(also popular in Cambridge at that time), the rules for each piece vary from game to game, and are initially kept secret from the players. Penultima
is similar in style to Eleusis
. The name of the game is a pun
on "penultimate", and "Ultima" (the name of the chess variant).
create secret rules which govern how the pieces move and two Players
attempt to discover these rules. The game is traditionally played with chess pieces but may be played with different pieces (e.g. Icehouse pieces
Before the game starts, the Spectators decide between themselves which pieces they will write rules for. The secret rule for a piece may for example control the way that piece moves, captures, or is captured, and may cause it to affect other pieces on the board. A piece may be given an invoke command which causes it to affect other pieces on the board without moving. When he or she has written the secret rule for a piece, the Spectator also gives it a new name for the duration of the game. These names (and the existence of any invoke commands) are announced to the players at the start of the game.
On his or her turn, a Player attempts to move or invoke one of their pieces, and the Spectator for that piece declares whether the action is legal or illegal. If it is legal, that Player's turn ends and play passes to the other Player. If it is illegal, the piece is returned to its position at the start of the turn. In the original game, play then passes to the other Player; in other variants the original Player continues making attempts until he or she succeeds in making a legal move or invoke.
As in standard chess, the winning player is the one who forces his or her opponent's king (or equivalent piece) into checkmate. At the end of the game, the Spectators reveal their rules.