Editing Rules of Go (section)

== Scoring systems ==
The most prominent difference between rulesets is the scoring method. There are two main scoring systems: territory scoring (the Japanese method) and area scoring (the Chinese method). A third system (stone scoring) is rarely used today but was used in the past and has historical and theoretical interest.

Care should be taken to distinguish between ''scoring'' systems and ''counting'' methods. Only two scoring systems are in wide use, but there are two ways of counting using "area" scoring.

=== Territory scoring ===
In territory scoring (including Japanese and Korean rules) a player's score is determined by the number of empty locations that player has surrounded minus the number of stones their opponent has captured.

Furthermore, Japanese and Korean rules have special provisions in cases of ''seki'', though this is not a necessary part of a territory scoring system. (See "[[Rules of go#Seki|Seki]]" below.)

Typically, counting is done by having each player place the prisoners they have taken into the opponent's territory and rearranging the remaining territory into easy-to-count shapes.

Territory scoring was how very old Chinese Go games were scored; Chinese style gradually switched to area scoring during the [[Yuan dynasty]] and [[Ming dynasty]] of the 13th&ndash;16th centuries.<ref>{{cite book |last=Fairbairn |first=John |date=2007 |editor-last=Finkel |editor-first=Irving L. |editor-link=Irving Finkel |title=Ancient Board Games in Perspective |publisher=The British Museum Press |pages=136 |chapter=Go in China |isbn= 9780714111537}}</ref>

=== Area scoring ===
In area scoring (including Chinese rules), a player's score is determined by the number of stones that player has on the board plus the empty area surrounded by that player's stones.

There are several common ways in which to count the score (all these ways will always result in the same winner):

* The oldest counting method is as follows: At the end of the game, all white stones are removed from the board, and the players use black stones to fill the entirety of the black territory. Score is determined by counting the black stones. Since the board contains 361 intersections, black must have 181 or more stones to win. This method is still widely used in [[Mainland China]].
* Around 1975, Taiwanese player and industrialist [[Ing Chang-ki]] invented a method of counting now known as Ing counting. Each player begins the game with exactly 180 stones (Ing also invented special stone containers that count each player's stones). At the end, all stones are placed on the board. One vacant intersection will remain, appearing in the winner's area; the number of stones of one color in the other color's area will indicate the margin of victory.

=== Stone scoring ===
In stone scoring, a player's score is the number of stones that player has on the board. Territory and prisoners are not counted. Play typically continues until both players have nearly filled their territories, leaving only the two eyes necessary to prevent capture. 

Stone scoring was likely the original method of Go scoring. It was described in a [[Dunhuang manuscripts|manuscript from Dunhuang]] from the [[Northern Zhou|Northern Zhou Dynasty]] (557–581), which is the oldest known Go manual.<ref name = name>{{Cite web|url = https://www.usgo-archive.org/sites/default/files/bh_library/historyofgorules.pdf|title = The History of Go Rules|author = Chen Zuyuan|year= 2011|access-date = 2024-07-29}}</ref> When Go reached Japan about 700 AD, the scoring system had been already streamlined—stone scoring had been replaced by territory scoring using the so-called ''group tax''.<ref>{{Cite web|quote = Around year 700, when the Chinese were still using territory scoring, go spread to Japan, and so the Japanese also came to play go with territory scoring. The Japanese then gradually altered the rules of the game, for example abolishing (...) the group tax.|url = https://www.nordicgodojo.eu/post/228/area-or-territory-a-brief-history-of-go-rules|author= Antti Törmänen |title = Area or territory – A brief history of go rules|year = 2020|access-date = 2024-07-29}}</ref> Stone scoring survived in some regions of China until the beginning of the 20th century.<ref>{{Cite web|url= https://www.usgo-archive.org/sites/default/files/bh_library/historyofgorules.pdf|title = The History of Go Rules|quote = This is stones scoring. In fact this rule was in use in China until the beginning of the last century (ang.).|author = Chen Zuyuan|year= 2011|access-date = 2024-07-29}}</ref>

===Group tax===
''Group tax'' means deducting one point for every eye needed for a group to survive.<ref name=Sensei>{{Cite web|url = https://senseis.xmp.net/?GroupTax|title = Group Tax|access-date=2024-07-29}}</ref> It equals two points for living groups and one point for groups in seki with one eye.<ref name=Sensei/> 

Group tax was a relic of stone scoring. Stone scoring includes it automatically since every (living) group needs two eyes and hence they cannot all be filled.<ref>{{Cite web|url = https://www.nordicgodojo.eu/post/228/area-or-territory-a-brief-history-of-go-rules|title =Area or territory – A brief history of go rules|author = Antti Törmänen |year = 2020|quote = [Group tax] was a byproduct of stone scoring: originally, only living scores counted towards a player’s score, so in the end the board was filled with stones; but every group has to leave two empty intersections for its eyes. Therefore, when the ‘group tax’ applies, every group costs a player two points.}}</ref>  Group tax was used with territory scoring both in Japan and in China.<ref name=Sensei/> In Japan it was abandoned because it made territory scoring convoluted.<ref>{{Cite web|url = https://www.nordicgodojo.eu/post/228/area-or-territory-a-brief-history-of-go-rules|title =Area or territory – A brief history of go rules|author = Antti Törmänen |year = 2020|quote = Therefore, when the ‘group tax’ applies, every group costs a player two points. This rule made the territory scoring process more convoluted, which is probably the main reason why it was abolished. }}</ref>   In China during the [[Ming Dynasty]] a new scoring system was devised: area scoring with group tax.<ref>{{Cite web|author =  Chen Zuyuan|year = 2011|title = The History of Go Rules|quote = So around the mid-Ming Dynasty, a new way of counting was invented: unilateral stones-counting on the overall 361 points. The total number of points on the board is 361, and we can count the total number of the stones and empty territory by one side, and compare it with the number 180.5. To be sure, eye points will have remained discounted, and in practice the score will have been amended with the difference between the numbers of both strings of living stones. |url = https://www.usgo-archive.org/sites/default/files/bh_library/historyofgorules.pdf}}</ref> The new system was equivalent to stone scoring. The group tax is likely the reason why eyes in seki aren't scored in the Japanese Rules.<ref name = Sensei/>

=== Attempts at reconciling the scoring systems ===
If the game ends with both players having played the same number of stones, then the result will be identical in territory and area scoring: indeed, the difference of stones on the board will equal the difference of prisoners and hence the difference of score will be the same.   

AGA rules call for a player to give the opponent a stone ("passing stone") when passing, and for White to play last (passing a third time if necessary).<ref>http://www.usgo.org/resources/downloads/completerules.pdf {{Bare URL PDF|date=March 2022}}</ref> Because of passing stones, when one player passes and the second makes a move the difference of prisoners changes exactly the same way as the difference of stones on the board. 

White's second pass is crucial when Black takes last dame. Since Black takes the last dame he made 1 move more than White. By taking the last dame Black gets 1 point under area scoring, but 0 points under territory scoring. To make territory and area scoring equal we need to give Black 1 additional point in territory scoring. Hence White's second pass. Thus, in AGA rules, the result using a territory system is always the same as it would be using an area scoring system.<ref>{{Cite web|url = https://www.britgo.org/files/rules/agasummary.pdf|title = AGA Rules Summary|quote = Area counting may only be used by prior agreement between both players. It will give exactly the same game result as the Territory Counting rules above.|author = Ron Bell|year= 2007|access-date = 2024-08-11}}</ref><ref>{{Cite web|url=https://www.cs.cmu.edu/~wjh/go/rules/AGA.commentary.html|title = The American Go Association Rules of Go: Commentary Appendix: Demonstration of the Relationship of Area and Territory Scoring|quote= This appendix shows that with normal play, under the given rules the "area" and "territory" scores of a game will always be the same. |date=1991-04-01|access-date =2024-08-11}}</ref>

The results for stone and area scoring are identical if both sides have the same number of groups. As mentioned above, the "[[#Group tax|group tax]]" used in some older rulesets of two points per group gave identical results to both territory and stone scoring.

=== Counting phase ===
Customarily, when players agree that there are no useful moves left (most often by passing in succession), they attempt to agree which groups are alive and which are dead. If disagreement arises, then under Chinese rules the players simply play on.

However, under Japanese rules, the game is already considered to have ended. The players attempt to ascertain which groups of stones would remain if both players played perfectly from that point on. (These groups are said to be ''alive''.) In addition, this play is done under rules in which kos are treated differently from ordinary play. If the players reach an incorrect conclusion, then they both lose.

The Japanese rules are accompanied by a lengthy commentary with examples of when groups are considered alive and when they are dead.<ref name="JapaneseRules"></ref> These examples do not cover every situation that may arise. Some difficult cases not entirely determined by the rules and existing precedent must be adjudicated by a go tribunal.{{Citation needed|date=March 2025|reason=Have go tribunals been needed since the rule change in 1989?}}

The need for the Japanese rules to address the definition of life and death follows from the fact that in the Japanese rules, scores are calculated by territory rather than by area. The rules cannot simply require a player to play on in order to prove that an opponent's group is dead, since playing in their own territory to do this would reduce their score. Therefore, the game is divided into a phase of ordinary play, and a phase of determination of life and death (which according to the Japanese rules is not technically part of the game).