Editing Rules of Go (section)

== Explanation of the basic rules ==
The object of the game of go is, in rough terms, to control more territory at the end of the game than one's opponent does.

=== Elements of the game ===

==== Players ====
'''Rule 1. Go is a game between two players, called Black and White.'''

The choice of black or white is traditionally done by chance between players of even strength. The method of selection is called ''nigiri''. One player (A) takes a handful of white stones; the other player (B) then places either one or two black stones on the board, indicating "even" or "odd". Player A counts the number stones in their hand to determine whether there is an odd or even number. If the number of stones matches the other player's selection of "even" or "odd", Player B will play the black stones; if not, they will take the white stones.

When players are of different strengths, the weaker player takes black. Black may also pre-place several handicap stones before play begins, to compensate for the difference in strength—see below.

==== Board ====
[[Image:Blank Go board.svg|right|thumb|250px|The board, or "goban"]]
'''Rule 2. Go is played on a plane grid of 19 horizontal and 19 vertical lines, called a ''board''.'''

'''Definition: A point on the board where a horizontal line meets a vertical line is called an ''intersection''. Two intersections are said to be ''adjacent'' if they are distinct and connected by a horizontal or vertical line with no other intersections between them.'''

The condition that the intersections be "distinct" is included to ensure that an intersection is not considered to be adjacent to itself.

Intersections are also called ''points''.

There are 361 points on a regular {{nowrap|19 × 19}} board.

For simplicity, the rules will be illustrated mostly using {{nowrap|5 × 5}} boards.

Each of the following diagrams shows two points on a {{nowrap|5 × 5}} board:

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  l|   |   |   |  r
|  l|  c|  c|   |  r
| dl|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  l|   |   |   |  r
| lc|   |   |   |  r
|dlc|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  l|   |   |   |  r
| lc|   |  c|   |  r
| dl|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |  c|  r
|  l|   |  c|   |  r
|  l|   |   |   |  r
| dl|  d|  d|  d| dr|24}}
|-valign="top"
|Adjacent points
|&nbsp;&nbsp;
|Adjacent points
|&nbsp;&nbsp;
|Non-adjacent points
|&nbsp;&nbsp;
|Non-adjacent points
|}

In the first two diagrams, the points are adjacent; in the third and fourth, they are not.

Though {{nowrap|19 × 19}} boards are standard, go can be played on another size board. Particularly common sizes for quick games are {{nowrap|9 × 9}} and {{nowrap|13 × 13}}. (See also "Board size" below.)

Beginners might prefer to play on a {{nowrap|9 × 9}} board to start. The nature of the game remains similar enough to make this worthwhile, yet the games are shorter. For beginners, playing longer games is less important than playing a greater number of games.

==== Stones ====
'''Rule 3. Go is played with playing tokens known as ''stones''. Each player has at their disposal an adequate supply of stones of their color.'''

Traditionally, Black is given 181 stones, and White, 180, to start the game. This is almost always sufficient, but if it turns out to be insufficient, extra stones will be used.

=== Positions ===
'''Rule 4. At any time in the game, each intersection on the board is in one and only one of the following three states: 1) empty; 2) occupied by a black stone; or 3) occupied by a white stone. A ''position'' consists of an indication of the state of each intersection.'''

Specifying a position involves only the current state of the board. It requires no indication of whose turn it is, nor any information relating to previous moves or states of the board. This definition of "position" is used in Rule 8 ("positional superko").

The diagram shows a possible position:

{{Go board 5x5
| ul|  b|  u|  u|  b
|  b|  b|   |  w|  b
|  l|   |  w|   |  r
|  w|   |  w|  b|  w
| dl|  b|  w|  w| dr|24}}

Naturally, two stones are said to be ''adjacent'' if they occupy adjacent intersections. Similarly, a stone and an intersection are ''adjacent'' if the stone occupies an intersection adjacent to that intersection.

==== Connected stones and points ====
'''Definition. Two placed stones of the same color (or two empty intersections) are said to be connected if it is possible to draw a path from one to the other by passing only through adjacent intersections of the same state (empty, occupied by white, or occupied by black).'''

The concept of connected stones is used to describe (via the concept of ''liberties'', defined below) the conditions in which stones are ''captured'' by a move. The concept of connected empty points is used only at the end of the game, to define a player's ''score''.

In the following position, the stones 1 and 7 are connected by the sequence of black stones 1, 2, ..., 7, in which each stone (other than 1) is adjacent to the stone before it. The empty points ''a'' and ''k'' are connected by the sequence of empty points ''a'', ''b'', ..., ''k'', in which each point (other than ''a'') is adjacent to the one before it. In fact, it is easy to see in this position that all the black stones are connected to each other and that all the empty points are connected to each other.

{{Go board 5x5
|ul|  u|  u|  u| ur
|lK|  J|  I|  H| rG
| l| b4| b5| b6| rF
| l| b3|  A| b7| rE
|b1| b2| dB| dC|drD|24}}

The following position can be used as an example for when stones and empty points are connected.

{{Go board 5x5
|ulA| b1| uF| uF| b4
| b1| b1|  F| w8| b4
| lB|  B| w6|  E| rE
| w5|  B| w6| b3| w7
|dlC| b2| w6| w6|drD|24}}

In the diagram, stones and empty points are marked with the same number or letter, respectively, whenever they are connected to each other.

A ''chain'' is a set of one or more stones (necessarily of the same color) that are all connected to each other and that are not connected to any other stones. Although it is not necessary to define the word ''chain'' in order to state the rules, the concept is important for an understanding of the game.

For example, Black and White each have four chains in the diagram above. Black has one three-stone chain, one two-stone chain, and two one-stone chains. White has one four-stone chain and three one-stone chains.

It follows from the definitions that any stone on the board belongs to exactly one chain. Furthermore, saying that two distinct stones of the same color are connected is the same as saying that they belong to the same chain.

==== Liberties ====
'''In a given position, a ''liberty'' of a stone is an empty intersection adjacent to that stone or adjacent to a stone which is connected to that stone.'''

For example:

{{Go board 5x5
| ul|  u| uD|  w|urC
|  l|  E| b4|  b| b3
|  w| b5|  b| b2| rB
|  w|  w| b1|  w|  r
| dl|  w| dA|  d| dr|24}}

In the above position, the points ''a'', ''b'', ''c'', ''d'', ''e'', are the liberties of the black stone at 1.
* ''a'' is a liberty of Black 1 because it is adjacent to Black 1 itself.
* ''b'' is a liberty of Black 1 because it is adjacent to Black 2, which is connected to Black 1. Alternatively, ''b'' is adjacent to Black 3.
* ''c'' is a liberty of Black 1 because it is adjacent to Black 3, which is connected to Black 1.
* ''d'' is a liberty of Black 1 because it is adjacent to Black 4, which is connected to Black 1.
* ''e'' is a liberty of Black 1 because it is adjacent to Black 5, which is connected to Black 1. Alternatively, ''e'' is adjacent to Black 4.

The results are the same when determining the liberties of Black 2, or of any other stone belonging to the black chain.

{{Go board 5x5
| ul|  u| uF| w7|urE
| lA|  G| b2| b2| b2
| w4| b3|  H| w6| rD
| w4| w4| b1| b1| b1
|dlB| w4| dC| w5| b1|24}}

In this position:
* The black stones marked 1 have the liberties ''c'', ''d'' and ''h''.
* The black stones marked 2 have the liberties ''d'', ''e'', ''f'', ''g'' and ''h''. 
* The black stone marked 3 has the liberties ''g'' and ''h''.
* The white stones marked 4 have the liberties ''a'', ''b'' and ''c''.
* The white stone marked 5 has the single liberty ''c''.
* The white stone marked 6 has the liberties ''d'' and ''h''.
* The white stone marked 7 has the liberties ''e'' and ''f''.

Since the liberties of any two stones belonging to the same chain are identical, they are often called the ''liberties'' of that chain. For example, in the first diagram, the points ''a'', ''b'', ''c'', ''d'' and ''e'' are the liberties of the lone black chain. In the second diagram, the liberties of the black chain in the lower right are ''c'', ''d'' and ''h''.

=== Play ===

==== Initial position ====
'''Rule 5. At the beginning of the game, the board is ''empty''.'''

==== Alternation of turns ====
'''Rule 6. Black moves first. The players alternate thereafter.'''

What players may do when they move is the object of Rules 7 and 8.

==== Moving ====
'''Rule 7. On their turn, a player may either pass (by announcing "pass" and performing no action) or play. A play consists of the following steps (performed in the prescribed order):'''
* Step 1. Placing a stone of their color on an empty intersection (chosen subject to Rule 8 and, if it is in effect, to Optional Rule 7A).
* Step 2. Removing from the board any stones of their opponent's color that have no liberties.
* Step 3. Removing from the board any stones of their own color that have no liberties.

A ''move'' is defined as a play or a pass. Thus, on each turn a player moves once.

A player may pass on any move. Usually, passing is beneficial only at the end of the game, when all territory has been claimed and further moves would be useless, or even harmful to a player's position.

The following three sections discuss the successive steps of a play in greater detail, bearing in mind that, in view of Steps 2 and 3, all stones remaining on the board after any move must have at least one liberty.

==== Placing a stone on the board ====
'''Step 1 of a play. The player places a stone of their color on an empty intersection (chosen subject to Rule 8 and, if it is in effect, to Optional Rule 7A).'''

As indicated by the reference to Rules 8 and 7A (respectively the superko rule and prohibition of suicide, to be discussed later), there are some restrictions on the choice of point at which to play.

The following diagrams show a possible sequence of moves at the beginning of the game:
{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  l|   |   |   |  r
|  l|   |   |   |  r
| dl|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   | b1|  r
|  l|   |   |   |  r
|  l|   |   |   |  r
| dl|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
|ul|  u|  u|  u| ur
| l|   |   |  b|  r
| l|   | w2|   |  r
| l|   |   |   |  r
|dl|  d|  d|  d| dr|24}}
|-valign="top"
|Start
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|White plays
|}

The following diagrams show how Black might play later in the same game:
{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  w| ur
|  l|  b|   |  b|  r
|  l|   |  w|   |  r
|  w|   |   |   |  r
| dl|  d|  d|  b| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  w| ur
|  l|  b| b1|  b|  r
|  l|   |  w|   |  r
|  w|   |   |   |  r
| dl|  d|  d|  b| dr|24}}
|&nbsp;&nbsp;
|-valign="top"
|Before
|&nbsp;&nbsp;
|After
|}

Numbers are often used, as here, to indicate new moves in printed diagrams.

Once a stone has been played, it remains on the board in the same location, until the end of the game or until it is captured (removed from the board as part of Step 2 or Step 3 of a play).

==== Capture ====
'''Step 2 of a play. (After playing their stone) a player removes from the board any stones of their opponent's color that have no liberties.'''

The stones removed from the board are said to have been ''captured'' by the player moving.

The diagrams below show the capture of a white stone by Black. To begin with, the white stone has a single liberty at ''a''. By playing a stone at ''a'', Black removes the last remaining liberty of the white stone. It is subsequently removed from the board.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  l|  b|  w|  A|  r
|  l|   |  b|   |  r
| dl|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  l|  b|  w| b1|  r
|  l|   |  b|   |  r
| dl|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  l|  b|   |  b|  r
|  l|   |  b|   |  r
| dl|  d|  d|  d| dr|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|After removal
|}

At the edge of the board and especially in the corners, stones have fewer liberties to start with and are more easily captured.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  b|   |   |   |  r
|  w|  b|   |   |  r
| lA|   |   |   |  r
| dl|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  b|   |   |   |  r
|  w|  b|   |   |  r
| b1|   |   |   |  r
| dl|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  b|   |   |   |  r
|  l|  b|   |   |  r
|  b|   |   |   |  r
| dl|  d|  d|  d| dr|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|After removal
|}

Next, White captures a chain of four black stones by playing at ''a''.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  w|  u|  u| ur
|  w|  b|  A|   |  r
|  w|  b|  b|  w|  r
|  l|  w|  b|  w|  r
| dl|  d|  w|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  w|  u|  u| ur
|  w|  b| w1|   |  r
|  w|  b|  b|  w|  r
|  l|  w|  b|  w|  r
| dl|  d|  w|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  w|  u|  u| ur
|  w|   |  w|   |  r
|  w|   |   |  w|  r
|  l|  w|   |  w|  r
| dl|  d|  w|  d| dr|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|White plays
|&nbsp;&nbsp;
|After removal
|}

Black captures the white chain by playing at ''a''. The black stone is not captured, because the white stones are removed first, providing it with two liberties.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  l|   |   |  b|  b
|  l|   |  b|  w|  w
| dl|  d|  b|  w|drA|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  l|   |   |  b|  b
|  l|   |  b|  w|  w
| dl|  d|  b|  w| b1|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  l|   |   |  b|  b
|  l|   |  b|   |  r
| dl|  d|  b|  d| b1|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|After removal
|}

Black captures the marked white chain at the edge of the board by playing at ''a''. Then White captures the black stone in the corner by playing at ''b''.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  l|  w|  w|  w|  r
|  l|   |  b|  b|  w
| dl|  b| wT| wT|drA|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  l|  w|  w|  w|  r
|  l|   |  b|  b|  w
| dl|  b| wT| wT| b1|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  l|  w|  w|  w|  r
|  l|   |  b|  b|  w
| dl|  b|  d| dB| b1|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  l|  w|  w|  w|  r
|  l|   |  b|  b|  w
| dl|  b|  d| w2| b1|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  l|  w|  w|  w|  r
|  l|   |  b|  b|  w
| dl|  b|  d| w2| dr|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|After capture
|&nbsp;&nbsp;
|White plays
|&nbsp;&nbsp;
|After capture
|}

Here, White captures the three marked black chains by playing at ''a''. 
{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  b|  b| ur
|  w|  w|   |  w|  r
|  w| bT|  w| bT|  w
| bT|  A| bT| bT|  w
| bT| bT|  w|  w| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  b|  b| ur
|  w|  w|   |  w|  r
|  w| bT|  w| bT|  w
| bT| w1| bT| bT|  w
| bT| bT|  w|  w| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  b|  b| ur
|  w|  w|   |  w|  r
|  w|   |  w|   |  w
|  l| w1|   |   |  w
| dl|  d|  w|  w| dr|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|White plays
|&nbsp;&nbsp;
|After capture
|}

==== Self-capture ====
'''Step 3 of a play. (After playing their stone and capturing any opposing stones) a player removes from the board any stones of their own color that have no liberties.'''

'''''Optional Rule 7A. A play is illegal if one or more stones would be removed in Step 3 of that play.'''''

The removal of one or more stones in Step 3 is called ''self-capture'', or ''suicide''. Most rulesets give effect to Optional Rule 7A, which prohibits it. This means that, in those rulesets, any play which under the basic rules would require a self-capture to be performed is illegal. For further information, see {{section link||Suicide}} below.

First an example which, it is emphasized, does ''not'' involve self-capture. When Black plays at ''a'', the capture of the marked white stones results in the black chain at the bottom right acquiring liberties. This move is legal (with the same result) whatever the rules.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  b|  b|  b|  b|  b
|  b| wT| wT| wT| wT
|  b| wT| dA|  b|  b|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  b|  b|  b|  b|  b
|  b| wT| wT| wT| wT
|  b| wT| b1|  b|  b|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  b|  b|  b|  b|  b
|  b|   |   |   |  r
|  b|  d| b1|  b|  b|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|After capture
|}

The previous example shows that it is important that Step 2 of a play (capture) precedes Step 3 (self-capture). If the order were reversed, then self-capture would occur here.

If a play results in the capture of opposing stones, self-capture will not occur. A newly placed stone only removes a liberty from chains which it is adjacent to; thus, a chain can only be captured if it contained a stone adjacent to the newly placed stone. The removal of that adjacent opposing stone creates a liberty for the newly placed stone, which is now a part of the chain(s) of its own color that lost a liberty when it was placed. Thus, all of those chains, which are now one chain, still have at least one liberty. 

Now some examples of plays in which self-capture occurs. These moves would be illegal under the optional rule prohibiting suicide.

In this example, if Black plays at ''a'', then the stone played by them is removed immediately. This move has the same effect on the position as a pass, though it would not allow White to end the game by passing next (Rule 9). The move is in any event illegal by Rule 8. (This is the positional superko rule. This move might be legal under other versions of the superko rule. See {{section link||Repetition}} below.)

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  b|   |  b|   |  r
|  w|  w|   |   |  r
|dlA|  w|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  b|   |  b|   |  r
|  w|  w|   |   |  r
| b1|  w|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  b|   |  b|   |  r
|  w|  w|   |   |  r
|dlA|  w|  d|  d| dr|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|After self-capture; violates Rule 8
|}

In the next example, Black plays at ''a'', resulting in the self-capture of the marked black stones.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  w|  u| ur
|  l|   |  b|   |  r
|  l|  b|  w|  w|  w
|  l|  w| bT|  A|  w
|  b|  d|  w| bT| bT|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  w|  u| ur
|  l|   |  b|   |  r
|  l|  b|  w|  w|  w
|  l|  w| bT| b1|  w
|  b|  d|  w| bT| bT|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  w|  u| ur
|  l|   |  b|   |  r
|  l|  b|  w|  w|  w
|  l|  w|   |  A|  w
|  b|  d|  w|  d| dr|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|After self-capture
|}

===={{anchor|Ko}} Ko and Superko====
{{main|Ko fight}}
'''Rule 8. A play is illegal if it would have the effect (after all steps of the play have been completed) of creating a position that has occurred previously in the game.'''

Though a pass is a kind of "move", it is not a "play". Therefore, Rule 8 never bars a player from passing. One consequence of Rule 8 is the so-called ''ko'' rule:

'''Consequence (ko rule). One may not play in such a way as to recreate the board position following one's previous move.'''

Whereas Rule 8 prohibits repetition of any previous position, the ko rule prohibits only ''immediate'' repetition.

The word ''ko'', pronounced with a long "o", is taken from [[Japanese language|Japanese]] ({{nihongo2|劫}}, {{Transliteration|ja|kō}}; usually written with [[katakana]]: {{nihongo2|コウ}}) and can mean both "threat" and "aeon" (from the Buddhist ''[[Kalpa (aeon)|kalpa]]'').<ref>[http://senseis.xmp.net/?KoEtymologyDiscussion Ko Etymology Discussion] {{Webarchive|url=https://web.archive.org/web/20051216102035/http://senseis.xmp.net/?KoEtymologyDiscussion |date=2005-12-16 }} at Sensei's Library</ref>

Rule 8 is known as the ''positional superko'' rule. The word "positional" is used to distinguish it from slightly different superko rules that are sometimes used. While the ko rule is observed in all forms of go, not all rulesets have a superko rule. The practical effects of the ko rule and the superko rule are similar; situations governed by the superko rule but not by the ko rule arise relatively infrequently. For further information, see {{section link||Repetition}} below.
 
The superko rule is designed to ensure the game eventually comes to an end, by preventing indefinite repetition of the same positions. While its purpose is similar to that of the [[threefold repetition]] rule of Western chess, it differs from it significantly in nature; the superko rule bans moves that would cause repetition, whereas Western chess allows such moves as one method of forcing a draw. It is more similar to the prohibition of moves which would repeat the position in Chinese Chess (Xiangqi). The ko rule has important strategic consequences in go.

Some examples follow in which Rule 8 applies. These examples cover only the most important case, namely the ko rule.

The first diagram shows the board immediately after White has played at 1, and it is Black's turn. Black captures the marked white stone by playing at ''a''. If White responds by capturing at ''b'' with 3, the board position is identical to that immediately following White 1. White 3 is therefore prohibited by the ko rule.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  b|  w|  u| ur
|  b| wT|  A|  w|  r
|  l|  b|  w|   |  r
|  l|   |  b| w1|  r
| dl|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  b|  w|  u| ur
|  b|  B| b2|  w|  r
|  l|  b|  w|   |  r
|  l|   |  b| w1|  r
| dl|  d|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  b|  w|  u| ur
|  b| w3|   |  w|  r
|  l|  b|  w|   |  r
|  l|   |  b| w1|  r
| dl|  d|  d|  d| dr|24}}
|-valign="top"
|Black to move
|&nbsp;&nbsp;
|Black captures
|&nbsp;&nbsp;
|Illegal recapture
|}

Another example of ko follows. Here, Black 3 is illegal by the ko rule.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l| b1|  b|   |  r
|  l|   |  w|   |  r
|  l|   |   |  w|  b
| dl|  d|  w| bT| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l| b1|  b|   |  r
|  l|   |  w|   |  r
|  l|   |   |  w|  b
| dl|  d|  w|  d| w2|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l| b1|  b|   |  r
|  l|   |  w|   |  r
|  l|   |   |  w|  b
| dl|  d|  w| b3| dr|24}}
|-valign="top"
|White to move
|&nbsp;&nbsp;
|White captures
|&nbsp;&nbsp;
|Illegal recapture
|}

As noted in the section "Self-capture", Rule 8 prohibits the suicide of a single stone. This is something of a triviality since such a move would not be strategically useful. Taking it for granted that no suicide of a single stone has occurred, the ko rule can be engaged in only one situation:

'''Restatement of the ko rule: One may not capture just one stone if that stone was played on the previous move and that move also captured just one stone.'''

Furthermore, this can occur only when one plays in the location at which one's stone was captured in the previous move. The two points where consecutive captures might occur, but for the ko rule, are said to be ''in ko''. For example, in the first two diagrams above, the points ''a'' and ''b'' are in ko.

The next two examples involve capture and immediate recapture, but the ko rule is not engaged, because either the first or second capture takes more than one stone.

In the first diagram below, White must prevent Black from playing at ''a'', and does this with 1 in the second diagram. Black can capture the three stones in White 1's group by playing at ''b''. Black does this with Black 2 in the third diagram. White may recapture Black 2 by playing at ''a'' again, because the resulting position, shown in the fourth diagram, has not occurred previously. It differs from the position after White 1 by the absence of the two marked white stones.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  w|  w|  b|  b
|  w|   |  w|  w|  b
|  l|  w|  w|  b|  b
| lA|  b|  b|   |  b
| wT| wT|  b|  b|  b|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  w|  w|  b|  b
|  w|   |  w|  w|  b
| lB|  w|  w|  b|  b
| w1|  b|  b|   |  b
| wT| wT|  b|  b|  b|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  w|  w|  b|  b
|  w|   |  w|  w|  b
| b2|  w|  w|  b|  b
| lA|  b|  b|   |  b
| dl|  d|  b|  b|  b|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  w|  w|  b|  b
|  w|   |  w|  w|  b
| lB|  w|  w|  b|  b
| w3|  b|  b|   |  b
| dl|  d|  b|  b|  b|24}}
|-valign="top"
|White to move
|&nbsp;&nbsp;
|White sacrifices
|&nbsp;&nbsp;
|Black captures
|&nbsp;&nbsp;
|Recapture legal
|}

In the first diagram below, it is White's turn. White must prevent Black from connecting the marked stones to the others by playing at ''a''. The second diagram shows White's move. White is threatening to capture the marked black stones by playing at ''b''. In the third diagram, Black plays at ''b'' to prevent this, capturing White 1. However, by playing at ''a'' again, White can capture Black 2's group. This is not barred by the ko rule because the resulting position, shown in the fourth diagram, differs from the one after White 1 by the absence of the marked black stones. This kind of capture is called a ''snapback''.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
|  w|  w|  w|  u| ur
| bT| bT|   |  w|  w
|  w| bT|  A|  b|  b
|  w|  w|  b|  b|  r
| dl|  d|  b|  d|  b|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
|  w|  w|  w|  u| ur
| bT| bT|  B|  w|  w
|  w| bT| w1|  b|  b
|  w|  w|  b|  b|  r
| dl|  d|  b|  d|  b|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
|  w|  w|  w|  u| ur
| bT| bT| b2|  w|  w
|  w| bT|  A|  b|  b
|  w|  w|  b|  b|  r
| dl|  d|  b|  d|  b|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
|  w|  w|  w|  u| ur
|  l|   |  B|  w|  w
|  w|   | w3|  b|  b
|  w|  w|  b|  b|  r
| dl|  d|  b|  d|  b|24}}
|-valign="top"
|White to move
|&nbsp;&nbsp;
|White sacrifices
|&nbsp;&nbsp;
|Black captures
|&nbsp;&nbsp;
|White snaps back
|}

=====Ko threats=====
The next example is typical of real games. It shows how the ko rule can sometimes be circumvented by first playing elsewhere on the board.

The first diagram below shows the position after Black 1. White can capture the marked black stone by playing at ''a''. The second diagram shows the resulting position. Black cannot immediately recapture at ''b'' because of the ko rule. So Black instead plays 3 in the third diagram. For reasons that will become clear, Black 3 is called a "ko threat".

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| b1|  u|  b|  w|  w
|  l|  b|  b|  w|  r
|  b|  b|  w|  w|  r
|  b|  A| bT|  w|  r
|  b|  b|  w|  w| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| b1|  u|  b|  w|  w
|  l|  b|  b|  w|  r
|  b|  b|  w|  w|  r
|  b| w2|  B|  w|  r
|  b|  b|  w|  w| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| b1|  u|  b|  w|  w
|  l|  b|  b|  w|  r
|  b|  b|  w|  w| b3
|  b| w2|  B|  w|  r
|  b|  b|  w|  w| dr|24}}
|-valign="top"
|White to move
|&nbsp;&nbsp;
|White captures
|&nbsp;&nbsp;
|Black plays away from the ko
|}

At this point, White could choose to connect at ''b'', as shown in the first diagram below. However, this would be strategically unsound, because Black 5 would guarantee that Black could eventually capture the white group altogether, no matter how White played.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| b1|  u|  b|  w|  w
|  l|  b|  b|  w|  r
|  b|  b|  w|  w| b3
|  b| w2| w4|  w|  r
|  b|  b|  w|  w| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| b1|  u|  b|  w|  w
|  l|  b|  b|  w|  r
|  b|  b|  w|  w| b3
|  b| w2| w4|  w| b5
|  b|  b|  w|  w| dr|24}}
|-valign="top"
|White 4 is an error
|&nbsp;&nbsp;
|Black takes advantage
|}

Instead, White responds correctly to Black 3 with 4 in the first diagram below. Now, contrary to the situation after White 2, Black can legally play at ''b'', because the resulting position, shown in the second diagram, has not occurred previously. It differs from the position after Black 1 because of the presence of Black 3 and White 4 on the board. Now White is prohibited from recapturing at ''a'' by the ko rule. White has no moves elsewhere on the board requiring an immediate reply from Black (ko threats), so White plays the less urgent move 6, capturing the black stone at 3, which could not have evaded capture even if White had waited. In the next diagram, Black connects at ''a'' before White has a chance to recapture. Both players pass and the game ends in this position.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| b1|  u|  b|  w|  w
|  l|  b|  b|  w|  r
|  b|  b|  w|  w| b3
|  b| w2|  B|  w| w4
|  b|  b|  w|  w| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| b1|  u|  b|  w|  w
|  l|  b|  b|  w|  r
|  b|  b|  w|  w| b3
|  b|  A| b5|  w| w4
|  b|  b|  w|  w| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| b1|  u|  b|  w|  w
|  l|  b|  b|  w| w6
|  b|  b|  w|  w|  r
|  b|  A| b5|  w| w4
|  b|  b|  w|  w| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| b1|  u|  b|  w|  w
|  l|  b|  b|  w| w6
|  b|  b|  w|  w|  r
|  b| b7| b5|  w| w4
|  b|  b|  w|  w| dr|24}}
|-valign="top"
|White replies to threat
|&nbsp;&nbsp;
|Black recaptures legally
|&nbsp;&nbsp;
|Ko bars recapture at ''a''
|&nbsp;&nbsp;
|Black connects
|}

=== End ===
'''Rule 9. The game ends when both players have passed consecutively. The ''final position'' (the position later used to score the game) is the position on the board at the time the players pass consecutively.'''

Since the position on the board at the time of the first two consecutive passes is the one used to score the game, Rule 9 can be said to require the players to "play the game out".

Under Rule 9, players must for example capture enemy stones even when it may be obvious to both players that they cannot evade capture. Otherwise the stones are not considered to have been captured. Because Rule 9 differs significantly from the various systems for ending the game used in practice, a word must be said about them.

These systems, which are discussed more fully in {{section link||Counting phase}} below, generally allow the game to end as soon as it is clear to the players which stones would remain on the board if the game continued. The precise means of achieving this varies widely by ruleset, and in some cases has strategic implications. These systems often use passing in a way that is incompatible with Rule 9. For players, knowing the conventions surrounding the manner of ending the game in a particular ruleset can therefore have practical importance.

Under Chinese rules, and more generally under any using the area scoring system, a player who played the game out as if Rule 9 were in effect would not be committing any strategic errors by doing so. They would, however, likely be viewed as unsportsmanlike for prolonging the game unnecessarily. On the other hand, under a territory scoring system like that of the Japanese rules, playing the game out in this way would in most cases be a strategic mistake.

==== Territory ====
'''Definition. In the final position, an empty intersection is said to belong to a player's territory if all stones adjacent to it or to an empty intersection connected to it are of that player's color.'''

''Note:'' Unless the entire board is empty, the second condition – that there be at least one stone of the kind required – is always satisfied and can be ignored.

A point can never belong to both players' territories.

On the other hand, it may well happen that an empty intersection belongs to neither player's territory. In that case the point is said to be ''neutral territory''.<ref>[https://www.cs.cmu.edu/~wjh/go/rules/AGA.html AGA Official Rules of Go]: "Neutral Points: Any empty points left on the board at the end of the game which are ''not'' completely surrounded by either player's stones are known as ''neutral points'', and are not counted toward either player's territory or area."</ref> There are rarely any more than a handful of neutral points at the end of a game; in the majority of cases, there are none at all.

Japanese and Korean rules count some points as neutral where the basic rules, like Chinese rules, would not. For more on this, see {{section link||Seki}}.

In order to understand the definition of territory, it is instructive to apply it first to a position of a kind that might arise before the end of a game.<ref>Position after move 45 of 53 in a game taken from the go rules of the First World Mind Sports Games. [http://www.intergofed.org/wmsg/members_documents/2008_July_16/WMSG-GoRule-Appendix1_Revised.pdf]</ref>
{{Goban 9x9

| |  | b|uI| b|uE| |uD|urC
| | b| H| b| w|  | | w| 
| | b| b| w| w|  | |  |w
| |  | b| b| w|  |w| w|b
| |  | b| w|  |  |w| b|b
| | X| X| B| w| w|b| J|b
| | X| b|  | w| b|b| b|b
| | X| b| w| w| w|b| F|w
| |dX|dA| b|dG| w|b| w|drK

|24|u=u|d=d|l=l|r=r}}

The point ''a'' is adjacent to a black stone. Therefore, ''a'' does not belong to White's territory. However, ''a'' is connected to ''b'' (by the path shown in the diagram, among others), which is adjacent to a white stone. Therefore, ''a'' does not belong to Black's territory either. In conclusion, ''a'' is neutral territory.

The point ''c'' is connected to ''d'', which is adjacent to a white stone. But ''c'' is also connected to ''e'', which is adjacent to a black stone. Therefore, ''c'' is neutral territory.

Similarly, the points ''f'' and ''g'' are neutral territory.

On the other hand, ''h'' is adjacent only to black stones and is not connected to any other points. Therefore, ''h'' is black territory. For the same reason, ''i'' and ''j'' are black territory, and ''k'' is white territory.

It is because there is so much territory left to be claimed that skilled players would not end the game in the previous position. The game might continue with White playing 1 in the next diagram. If the game ended in this new position, the marked intersections would become White's territory, since they would no longer be connected to an empty intersection adjacent to a black stone. 
{{Goban 9x9

| | |b| |b|w1|uX|uX|urX
| |b| |b|w| X| X| w|rX
| |b|b|w|w| X| X| X|w
| | |b|b|w| X| w| w|b
| | |b|w|X| X| w| b|b
| | | | |w| w| b|  |b
| | |b| |w| b| b| b|b
| | |b|w|w| w| b|  |w
| | | |b| | w| b| w|

|24|u=u|d=d|l=l|r=r}}

The game might end with the moves shown below. In the final position, the points marked ''a'' are black territory and the points marked ''b'' are white territory. The point marked ''c'' is the only neutral territory left.
{{Goban 9x9

|ulA|uA| b|b1| b|w|uB|uB|urB
| lA| b| A| b| w|B| B| w|rB
| lA| b| b| w| w|B| B| B|w
| lA| A| b| b| w|B| w| w|b
| lA| A| b| w| B|B| w| b|b
| lA|b3|w2|w4| w|w| b| A|b
| lA| A| b|w6| w|b| b| b|b
| lA| A| b| w| w|w| b| C|w
|dlA|dA|b5| b|b7|w| b| w|drB

|24|u=u|d=d|l=l|r=r}}

In Japanese and Korean rules, the point in the lower right corner and the point marked ''a'' on the right side of the board would fall under the ''seki'' exception, in which they would be considered neutral territory. (See {{section link||Seki}} below.)

==== Area ====
'''Definition. In the final position, an intersection is said to belong to a player's ''area'' if either: 1) it belongs to that player's territory; or 2) it is occupied by a stone of that player's color.'''

Consider once again the final position shown in the last diagram of the section "Territory". The following diagram illustrates the area of each player in that position. Points in a player's area are occupied by a stone of the corresponding color. The lone neutral point does not belong to either player's area.  
{{Goban 9x9

|b|b|b|b|b|w|w|w|w
|b|b|b|b|w|w|w|w|w
|b|b|b|w|w|w|w|w|w
|b|b|b|b|w|w|w|w|b
|b|b|b|w|w|w|w|b|b
|b|b|w|w|w|w|b|b|b
|b|b|b|w|w|b|b|b|b
|b|b|b|w|w|w|b| |w
|b|b|b|b|b|w|b|w|w

|24|u=u|d=d|l=l|r=r}}

==== Score ====
'''Definition. A player's ''score'' is the number of intersections in their area in the final position.'''{{dubious|What about komidashi? What about different scoring systems? Ehh?|date=February 2014}}

For example, if a game ended as in the last diagram in the section "Territory", the score would be: Black 44, White 36. The players' scores add to 80. The difference between this and the 81 intersections on a {{nowrap|9 × 9}} board is accounted for by the one point of neutral territory.
 
The scoring system described here is known as ''area scoring'', and is the one used in the Chinese rules. Different scoring systems exist. These determine the same winner in most instances. See the ''Scoring systems'' section below.

==== Winner ====
'''Rule 10. If one player has a higher score than the other, then that player wins. Otherwise, the game is drawn.'''

In the previous example, Black wins by eight points.

Margin of victory does not matter; winning by one point is as good as winning by 100 points.