Go variants

There are many variations on the basic game of . Some are ancient digressions, whilst other are modern deviations. They are often to be found as side events at tournaments, for instance the , has a "Crazy Go" evening scheduled each year.

=Variants=

National variants

The difficulty in defining the rules of Go has led to a situation where there are many subtly different rulesets in existence. They are distinct over such areas as scoring method, ko, suicide, handicap placement and what to do about neutral points at the end of the game. In the main these differences are small enough to avoid changing the character and strategy of the game, so we do not consider them here. For more info refer to: Go rules.

There are some versions that are so distinct as to be considered variants. In other cases the effect of rule differences on actual play is minor, but for these the tactical consequences are substantive.

Tibetan Go

is played on a 17×17 board, six stones from each colour are placed on the third line, as shown. White makes the first move. There is a unique ko rule: ''one may not play a stone at an intersection where the opponent has just removed a stone''. This ko rule is so different from the other major rulesets, that it alone significantly changes the character of the game. Finally, a player who controls all four corner points gets a bonus of 40 points, and if he also controls the centre point he gets a further bonus of 10 points.

There is an additional rule for a subvariant played within Tibet. It is forbidden to play more than 2 intersections either from the last stone placed on the board, or from one of your own Bo.

Sunjang Baduk

A different form of Go evolved in Korea called sunjang baduk. What there is, tells us that has at least been played from the 7th century. Its most distinctive feature is the prescribed opening. The starting position dictates the placement of 16 stones as shown, and the first move is prescribed for Black at the center of the board. However, the counting system for determining territory at the end of the game also has some important differences. Namely, stones internal to territory and irrelevant to boundary definition, are removed before counting territory.

Variants altering the rules of play

First Capture

The first player to capture a stone wins. It was invented by Japanese professional Yasutoshi Yasuda who describes it in his book . Yasuda was first inspired by the need for a medium to address the problem of bullying in Japan, but soon found that "First Capture" also works as an activity with senior citizens and even developmentally delayed individuals. He sees it as a game in its own right, not just as a prelude to Go, but also as a way to introduce simple concepts that lead to Go. For the latter purpose, he recommends progressing to "Most Capture", in which the player capturing the most stones wins; then it is natural to introduce the idea of capturing territory, not just the opponent's stones. This variation is often called ''Atari Go'' in the West, were it is becoming increasingly popular as a preliminary means of introducing Go itself to beginners.

Environmental Go

, invented by Elwyn Berlekamp, adds an element of mathematical precision to the game. In lieu of playing a stone, a player may take the highest remaining card from a pack of cards valued in steps of ? from ? to 20: the player's score will be the territory captured, plus the total value of cards taken. In effect, the players participate in a downward auction for the number of points they think ''sente'' is worth at each stage in the game.
The professional players Jiang Zhujiu and Rui Naiwei played the first Environmental Go game in April 1998. Since then the variant has seen little activity on the international scene.

Cards Go

In players draw from a pack of cards contain instructions to play one of a fixed set of commonly occurring shapes. If the said shape cannot be placed on the board, then an illegal move is deemed to have been played: this necessitates resignation.

Multi-player Go

In ''Multi-player Go'', stones of different colors are used so that four players or more can play on one board.

Variants for more than two players, but not altering the mechanism of the game

Rengo

This involves two teams of players taking either the Black or the White stones. Each player in the team must play in turn, playing out of sequence will normally result in a small penalty . Partners may not consult on how to play, or engage in any form of signalling. Communication between partners may only take the following forms listed below.

* ''May we resign?'' can be answered with ''yes'' or ''no''
* ''How much time is left?''
* ''Whose turn is it?''

Pair Go

is a gender specific form of Rengo, calling for teams composed of one male and one female member. It was popularised by the Japan Pair Go Association as a means of increasing female participation in the game. They hoped that this increase in itself would add a new appeal to the game. They first introduced the variant to Europe at the 1992 European Congress in Canterbury, England. The International Pair Go Association sponsors an annual in Tokyo in November which has been running uninterrupted since 1989. The first professional Pair Go world championship was held in 1994.

''Note that BGA records suggest the first Pair Go tournament was held in 1991, which is a direct contradiction of the International Pair Go website''

Variants requiring a memory of the position

Blind Go

One or both of the players cannot see the board in this variant. Therefore they have to remember the whole position. This is considered much more difficult than playing blind chess. Indeed, most club standard players can play blind chess, but only professional players are able to complete a game of blind 19×19 Go.

One Color Go

Both players use stones of the same color. This variation is regarded as a useful tool for developing one's reading skills.

Variants with limited knowledge of the position

These variants are not purely strategic games, as the element of luck is quite important.

Shadow Go

This game requires two players, a referee and three playing sets. Each player sees only his own board, while the referee can see them both and also have his own set. Players place stones on their boards, with no knowledge of what other players are doing. A referee keeps track of the game on the central board. If any player makes an illegal move, the referee informs him about it . The player is allowed to make another move.

Rengo Kriegspiel

This is a crossover between rengo and shadow Go. There are four players, a referee and five Go sets. Each player has a limited knowledge not only about enemy stones, but also his teammate stones.

Non-standard boards

Although Go is most commonly played on a board with 19×19 lines, 9×9 and 13×13 boards are also available. They are used by beginners and by players who want a game that finishes more quickly. Due to flexibility of configuration, the two smaller sizes are more often played on the online Go servers such as KGS Go Server, which allows board sizes from 2×2 to 38×38.

The annual Milton Keynes Go Tournament has a popular side event which is played on a stylised map of Milton Keynes. The "Milton Keynes" board can be found , its non-conventional lattice presents some interesting possibilities. Another variant in this fashion is the .

A board is two dimensional surface with an implied third dimension because it is as if a standard board has been rolled and two opposite edges joined to form a tube and then the ends of the tube joined. It can be simulated on a standard 19×19 board, but requires imagination on the part of the players to perform an abstract join at the edges. It is noteworthy that the toroidal board has no corners, so standard joseki do not apply.

''TriGo'' is a go variant that uses a triangular-grid goban, where each stone has up to six liberties. To compensate for this, there are several rule changes: and superko are limited in scope, is not used, and after the first stone is placed, every turn consists of placing two stones. After both players have passed a turn, the score is counted , and in the case of a draw the player passing first wins.

Other than 2D

Alak is a Go-like game restricted to a single spatial dimension.

Go can be extended to . An example is , using the structure of a diamond crystal lattice. With many Go variants, the nature of the game changes dramatically if they do not keep the standard 4-connectivity of the points, which Diamond Go maintains.