Phantom Go is a variant of Go for two players and a referee.
Each player has his own board, set up so that they can't see the other player's board. The referee has a board of his own.
To make a move, a player plays a stone on his own board. The referee then checks on his board whether the move is legal and informs both players about the tried move. As long as a player tries to play an illegal move (such as on a nonempty intersection, or suicide, or capturing back a ko), it's still his turn and he may try another move.
After the player has made a legal move, the referee copies the move to his own board. Then, it's the other player's turn.
There are different rule sets regarding what exactly the referee says in which situation (see below).
For speed, the game is best played on a 9x9 or 13x13 board.
If the move could be performed normally he says: 'Black has moved'
If the move was illegal he says 'Illegal move' (but not whether the move was illegal due to a stone already being present or because of the suicide rule).
If the move leads to capture, the referee says 'Black has captured the following stones ...' after which he points out exactly which stones where captured to the White player (and to Black should that be necessary).
To give fair warning to the players the referee also warns when groups are first put into atari.
A snapback sounds like this:
- Black plays and puts a white group into atari.
- White captures one stone and puts himself into atari.
- Black captures seventeen stones.
Hamburg Referee Rules
The referee answers each try with one of the following comments:
- Black/White has moved, White/Black to move.
- Black/White [captures n stones and] puts White/Black [and himself] into atari.
- There is already an opponent’s stone.
- There is already an own stone.
- The ko cannot be captured back immediately.
- Black/White passes.
Note that the referee does NOT say:
- Which of the stones have been put into atari.
- How many stones have been put into atari.
- Which of the stones have been captured.
Phantom Go needs a lot of physical space since the players sit back-to-back and the referee stands between them. Each of them needs a table with a board and bowls.
There is an Android app called Phantom Go that allows two players to play Phantom Go using a single phone or tablet.
Bill: I have played a form of this game, which we called Kriegspiel Go, after the similar chess variant. The referee only informed the players when it was their turn, prevented illegal moves (the opponent could hear him do that), and removed captured stones. A 9x9 board was large enough. ;-)
Jan: I've also played it that way, but the information about ataris tends to speed up the game and provides some extra confusion... I'm the second best Phantom Go player in Utrecht, by the way :-)
Phantom Go was played in New Zealand from about the late 1970s but I don't know if we invented it or not.
Phelan: I had read the article before, and it seems to disregard the fact that the computer player would be much better at keeping the board in memory. It just needs to record the result of its moves to get a picture of the board. A human would have to deal with faulty memory. It would at least require much more memorization skills than usually, probably comparable to the efforts of blind go players.
If i understand correct, then the point is to find a position where either enemy stone is present, or if it's not, it's good place to play. Thus it might be good to try and check as many positions in a move as possible. Unless a failure durng piece placement means you pass a turn. This already, in an elegant way, introduces a common factor of "fog of war" games - deception. I can place my pieces in a way that would be most foolish in ordinary Go, but it will trick my oponnent into expecting one of several other formations. He should be then tricked into placing a stone in position favorable for me. -- e7th04sh