Rules of Go

Rules Of Igo

This is an in-depth discussion of the rules of go.

There has been a certain amount of variation in the rules of go over time, and from place to place. This article discusses those sets of rules broadly similar to the ones currently in use in East Asia. (Traditional Himalayan variants, including Tibetan go, differ more markedly and are discussed instead in the article Go variants.) Even among these, there is a degree of variation.

Notably, Chinese and Japanese rules differ in a number of respects. The most significant of these is the scoring method, together with attendant differences in the manner of ending the game.

While differences between sets of rules may have moderate strategic consequences on occasion, they do not change the character of the game. The different sets of rules usually lead to the same game result, so long as the players make minor adjustments near the end of the game.

This article first presents a simple set of rules which are, except for wording, identical to those usually referred to as the Tromp-Taylor Rules, themselves close in most essential respects to the Chinese rules. These rules are then discussed at length, in a way that does not assume prior knowledge of go on the part of the reader. The discussion is for the most part applicable to all sets of rules, with exceptions noted. Later sections of the article address major areas of variation in the rules of go, and individual sets of rules.

Basic rules

Basic rules

One black chain and two white chains, their liberties shown with dots. Note that liberties are shared among all stones of a chain.

Two players, Black and White, take turns placing a stone (game piece) of their own color on a vacant point (intersection) of the grid on a Go board. Black moves first. (If there is a large difference in strength between the players, Black is sometimes allowed to place two or more stones on the board for his first move, see Go handicaps for details). The official grid comprises 19×19 lines, though the rules can be applie

d to any grid size; 13×13 and 9×9 are popular choices to teach beginners. Once played, a stone may not be moved to a different point.

Vertically and horizontally adjacent stones of the same color form a chain (also called a group) that shares its liberties (see below) in common, cannot subsequently be subdivided, and in effect becomes a single larger stone. Only stones connected to one another by the lines on the board create a chain; stones that are diagonally adjacent are not connected. Chains may be expanded by playing additional stones on adjacent intersections or connected together by playing a stone on an intersection that is adjacent to two or more chains of the same color.

If white plays at A, the black chain loses its last liberty. It is captured and removed from the board.

A vacant point adjacent to a stone is called a liberty for that stone. Chains of stones share their liberties. A chain of stones must have at least one liberty to remain on the board. When a chain is surrounded by opposing stones so that it

has no liberties, it is captured and removed from the board.

Most rule sets do not allow a player to play a stone in such a way that one of their own chains is left without liberties, subject to the following important exception. The rule does not apply if playing the new stone results in the capture of one or more of the opponent's stones. In this case, the opponent's stones are captured first, leaving the newly played stone at least one liberty.The rule just stated is said to prohibit suicide. (Since suicide is very rarely useful, making it legal does not significantly alter the nature of the game.)

An example of a situation in which the ko rule applies

Players are not allowed to make a move that returns the game to the position before the opponent's last move. This rule, called the ko rule (from the Japanese 劫 kō "eon"), prevents unending repetition.See the example to the right: Black has just played the stone marked 1, capturing a white stone at the intersection marked with a circle. If White were now allowed to play on the marked intersection, that move would capture the black stone marked 1 and recreate the situation before Black made the move marked 1. Allowing this could result in an unending cycle of captures by both players. The ko rule therefore prohibits White from playing at the marked intersection immediately. Instead White must play elsewhere; Black can then end the ko by filling at the marked intersection, creating a five-stone Black chain. If White wants to continue the ko, White will try to find a play that Black must answer; if Black answers, then White can retake the ko. A repetition of such exchanges is called a ko fight.

While the various rule sets agree on the ko rule prohibiting returning the board to an immediately previous position, they deal in different ways with the relatively uncommon situation in which a player might recreate a past position that is further removed. See Rules of Go: Repetition for further information.

Instead of placing a stone, a player may pass. This usually occurs when they believe no useful moves remain. When both players pass consecutively, the game ends and is then scored.

Introduction igo

Go is a strategic board game for two players. Also known as igo (Japanese), weiqi or wei chi (Chinese) or baduk (korea). Go noted for being rich in strategic complexity despite the simple rules.

Like a chess game played by two players who alternately place black and white stones (play fruits, now usually made of glass or plastic) at the intersection of a box of empty 19 × 19 rows. The purpose of this game is to control a larger portion of the board than your opponent. A stone or group of stones that were captured and removed if it does not have an empty adjacent intersection, the result is completely surrounded by stones of the opposite color.

Placing stones close together helps them support each other and avoid capture. On the other hand, placing stones far apart creates more influence on the board. Part of the strategic difficulty of the game comes from finding a balance between conflicting interests like that. Players strive to serve both defensive and offensive purposes and choose between tactical urgency and strategic plans.

Go originated from ancient China over 2,500 years ago, and although it is not known exactly when the game was created, in the 3rd century BC it had become a popular hobby, as indicated by the reference to the game in the Analects of Confucius. Archaeological evidence indicates that the initial game is played on a board with 17 × 17 grid, but at the time that the game spread to Korea and Japan at approximately the 7th century to the board 19 × 19 grid has become the standard.

The most popular game in East Asia, but has gained some popularity in other parts of the world in recent years. A conservative estimate places the number of go players in the world at around 27 million. Go to reach the West through the Japanese, which is why it is generally recognized internationally by the Japanese name.

Equipment of Igo

It is possible to play Go with a simple paper board and coins or plastic tokens for the stones. More popular midrange equipment includes cardstock, a laminated particle board, or wood boards with stones of plastic or glass. More expensive traditional materials are still used by many players.

Traditional equipment

Boards


















The Go board - generally referred to by its Japanese name goban - typically measures between 45 cm (17.7 in) and 48 cm (18.9 in) in length (from one player's side to the other) and 42 cm (16.5 in) to 44 cm (17.3 in) in width. Chinese boards are slightly larger, as a traditional Chinese Go stone is slightly larger to match. The board is not square; there is a 15:14 ratio in length to width, because with a perfectly square board, from the player's viewing angle the perspective creates a foreshortening of the board. The added length compensates for this.[36] There are two main types of boards: a table board similar in most respects to other game boards like that used for chess, and a floor board, which is its own free-standing table and at which the players sit.

The traditional Japanese goban is between 10 cm (3.9 in) and 18 cm (7.1 in) thick and has legs; it sits on the floor (see picture to right), as do the players.[36] It is preferably made from the rare golden-tinged Kaya tree (Torreya nucifera), with the very best made from Kaya trees up to 700 years old. More recently, the related California Torreya (Torreya californica) has been prized for its light color and pale rings, as well as its less expensive and more readily available stock. The natural resources of Japan have been unable to keep up with the enormous demand for the slow-growing Kaya trees; both T. nucifera and T. californica must be of sufficient age (many hundreds of years) to grow to the necessary size, and they are now extremely rare at the age and quality required, raising the price of such equipment tremendously.[37] In Japan, harvesting of live Kaya trees is banned, as the species is protected; the tree must die of natural causes before it is harvested. Thus, an old-growth, floor-standing Kaya goban can easily cost in excess of US$10,000 with the highest-quality examples costing more than $60,000.[38]

Other, less expensive woods often used to make quality table boards in both Chinese and Japanese dimensions include Hiba (Thujopsis dolabrata), Katsura (Cercidiphyllum japonicum), Kauri (Agathis), and Shin Kaya (various varieties of spruce, commonly from Alaska, Siberia and China's Yunnan Province).[37] So-called Shin Kaya is a potentially confusing merchant's term: shin means "new", and thus shin kaya is best translated "faux kaya"—the woods so described are biologically unrelated to Kaya.[37] Beginning in the early 2000s, some boards have been made by compositing strips of bamboo to create a material called "bamboo plywood" or "plybamboo". The resulting board is very durable and has a unique aesthetic, while being relatively inexpensive.


Stones

A full set of Go stones (goishi) usually contains 181 black stones and 180 white ones; a 19×19 grid has 361 points, so there are enough stones to cover the board, and Black gets the extra odd stone because that player goes first. There are two main types of stones: single-convex, in which one side is flat, and double-convex, in which both sides have a similar curve. Each type has its pros and cons: single-convex stones, placed flat side down, are less prone to move out of position if the board is bumped or disturbed by nearby movement. In addition, during post-game analysis, players can try out variations using upside-down stones, making it easy to remember the actual game moves. On the other hand, flat stones are harder to clear from the board at the end of the game.

Traditional Japanese stones are double-convex, and made of clamshell (white) and slate (black).[39] The classic slate is nachiguro stone mined in Wakayama Prefecture and the clamshell from the Hamaguri clam; however, due to a scarcity in the Japanese supply of this clam, the stones are most often made of shells harvested from Mexico.[39] Historically, the most prized stones were made of jade, often given to the reigning emperor as a gift.[39]

In China, the game is traditionally played with single-convex stones[39] made of a composite called Yunzi. The material comes from Yunnan Province and is made by sintering a proprietary and trade-secret mixture of mineral compounds. This process dates to the Tang Dynasty and, after the knowledge was lost in the 1920s during the Chinese Civil War, was rediscovered in the 1960s by the now state-run Yunzi company. The material is prized for its colors, its pleasing sound as compared to glass or to synthetics such as melamine, and its lower cost as opposed to other materials such as slate/shell. The term "yunzi" can also refer to a single-convex stone made of any material; however, most English-language Go suppliers will specify Yunzi as a material and single-convex as a shape to avoid confusion, as stones made of Yunzi are also available in double-convex while synthetic stones can be either shape.

Traditional stones are made so that black stones are slightly larger in diameter than white; this is to compensate for the optical illusion created by contrasting colors that would make equal-sized white stones appear larger on the board than black stones.

Bowls








The bowls for the stones are shaped like a flattened sphere with a level underside.[40] The lid is loose fitting and upturned before play to receive stones captured during the game. Chinese bowls are again slightly larger, and a little more rounded, a style known as Go Seigen; Japanese Kitani bowls tend to have a shape closer to that of the bowl of a snifter glass, such as for brandy. The bowls are usually made of turned wood. Rosewood is the traditional material for Japanese bowls, but is very expensive; wood from the Chinese jujube date tree, which has a lighter color (it is often stained) and slightly more visible grain pattern, is a common substitute for rosewood, and traditional for Go Seigen-style bowls. Other traditional Chinese bowls include lacquered wood bowls, or woven straw or rattan baskets. Stone bowls also are traditionally used. The names of the bowl shapes, Go Seigen and Kitani, pay homage to two 20th-century professional Go players by the same names, of Chinese and Japanese nationality, respectively, who are referred to as the "Fathers of modern Go".[41]

Modern and low-cost alternatives











In clubs and at tournaments, where large numbers of sets must be purchased and maintained by one organization, expensive traditional sets are not usually used. For these situations, table boards are usually used instead of floor boards, and are either made of a lower-cost wood such as spruce or bamboo, or are flexible mats made of vinyl that can be rolled up. In such cases, the stones are usually made of glass, plastic or resin (such as melamine or Bakelite) rather than slate and shell. Bowls are often made of plastic.

Common "novice" Go sets are all-inclusive kits made of particle board or plywood, with plastic or glass stones, that either fold up to enclose the stone containers or have pull-out drawers to keep stones. In relative terms, these sets are inexpensive, costing US$20


Playing technique and etiquette


The traditional way to place a Go stone is to first take one from the bowl, gripping it between the index and middle fingers, with the middle finger on top, and then placing it directly on the desired intersection.[42] It is considered respectful of the opponent to place the first stone to the player's upper right-hand corner. Although it can be soothing and pleasant to run one's hand through the bowl or hold a handful of stones, this can be noisy and unnerving to one's opponent; it is considered good form to take only one stone at a time as one decides where to play. It is permissible to strike the board firmly to produce a sharp click. Many consider the acoustic properties of the board to be quite important.[37] The traditional goban usually has its underside carved with a pyramid called a heso recessed into the board. Tradition holds that this is to give a better resonance to the stone's click, but the more conventional explanation is it allows the board to expand and contract without splitting the wood.[37] In theory, the wood never fully dries, so fully sealing it threatens warping in varying conditions. The heso allows the board to breathe.


Time control
See also: Time control and Byoyomi

A game of Go may be timed using a game clock. Formal time controls were introduced into the professional game during the 1920s and were controversial.[43] Adjournments and sealed moves began to be regulated in the 1930s. Go tournaments use a number of different time control systems. All common systems envisage a single main period of time for each player for the game, but they vary on the protocols for continuation (in overtime) after a player has finished that time allowance.[nb 5] The most widely used time control system is the so called byoyomi[nb 6] system. The top professional Go matches have timekeepers so that the players do not have to press their own clocks.

Two widely used variants of the byoyomi system are:[44]
Standard byoyomi: After the main time is depleted, a player has a certain number of time periods (typically around thirty seconds). After each move, the number of full time periods that the player took (possibly zero) is subtracted. For example, if a player has three thirty-second time periods and takes thirty or more (but less than sixty) seconds to make a move, they lose one time period. With 60–89 seconds, they lose two time periods, and so on. If, however, they take less than thirty seconds, the timer simply resets without subtracting any periods. Using up the last period means that the player has lost on time.
Canadian byoyomi: After using all of their main time, a player must make a certain number of moves within a certain period of time, such as twenty moves within five minutes.[44][nb 7] If the time period expires without the required number of stones having been played, then the player has lost on time.[nb 8]


Notation and recording games

Go games are recorded with a simple coordinate system. This is comparable to algebraic chess notation, except that Go stones do not move and thus require only one coordinate per turn. Coordinate systems include purely numerical ("4-4 point"), hybrid ("K3"), and purely alphabetical. The Smart Game Format uses alphabetical coordinates internally, but most editors represent the board with hybrid coordinates as this reduces confusion. The Japanese word kifu is sometimes used to refer to a game record.

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