Go

How to Play

Here we have a written version of an introductory lecture that used to be given at the first CUGOS meeting of each University year. It will teach a complete beginner everything necessary to play a game of 9x9 Go. We have also included a description of the rules of ko and seki for completion.

Introduction

This short course will introduce you to the rules of the Oriental board game Go. The rules of Go sometimes seem confusing at first sight but they are, in fact, very simple once you have played a few games.

One potential source of confusion is that slightly different versions of the rules are used in different countries. In practice this makes absolutely no difference to how the game is played or to what the final outcome is in 99.9% of games. The purpose of this page is to help members of the Cambridge University Go Society. They will therefore teach you the rules and conventions that are used in the United Kingdom.

At the start of each academic year the Cambridge Go Society gains 10-20 new members who have never played the game before. To teach them the rules we hold a series of 4 half hour talks at the start of our Tuesday meetings. This page contains the first of these lessons

You should be able to learn all the rules you need to play Go in this course. This is quite a lot to take in in half an hour so at the end I will summarise the important points. Once you have played a few games you will probably find that it all becomes second nature.

First of all I will show you the equipment used to play go. I will then show you that a move in the game consists of putting a counter of your colour on the board. Once a piece has been put on the board it is never moved. It can, however, be removed if it is captured, so I will then explain exactly how stones are captured by being surrounded.

Once I have shown you that pieces can be captured I will have to show you that not every single stone is destined to be captured in the end. I will then tell you about a simple game called 'capture go' which is useful for making sure that you understand the rules of capturing and how to stop your groups being captured.

I will then finally be able to tell you what the real point of go is: that is, to take territory. I will explain precisely what this means and how you work out who has won when the game ends.

The Basics

Go is a game of skill for 2 players. It is played on a square grid that looks something like this:

The moves are played on the points where the lines cross, not in the squares, so this is a 9x9 board. I strongly recommend that you play your first 10 to 20 games on a 9x9 board. After that you should play for a while on a 13x13 board. Only when you are really happy with the rules and the basic tactics is it worth moving to a full sized 19x19 board. The reason for using a smaller board at first is that the games do not last as long and so you will be able to play more games. You will learn much more from playing four 9x9 games that from playing one 19x19 game.

If you look closely you will notice that go boards are not absolutely square. they are slightly longer in one direction so that when you look at them sitting at a table they become slightly foreshortened and look square.

The game is played using black and white counters called 'stones'. Black moves first and play then alternates until the game ends. When it is your move you may either take a stone of your own colour and put it on any empty point (with one or two exceptions the will be explained in due course), or you may pass by saying "I pass". The game ends when both players pass consecutively. For example the first three moves of a game of go might be played at the points numbered 1, 2 and 3 in this diagram.

(This, by the way, is how games of go are normally recorded.)

Stones may, of course, be played right at the edge of the board or on the corners like moves 1 or 2 in the next diagram but it is normally bad to play this near the edge of the board at the start of the game.

Liberties and Capturing

Once a stone has been put on the board it is never moved. It may, however, be removed by being captured. This is the subject of this section.

I would like you to look at this stone in the middle of the board:

You can see that there are 4 empty points next to it. It is said to have 4 'liberties'. If a stone is on the edge of the board like this:

Then it only has 3 liberties. How many liberties does this stone have?

(Answer: 2)

If white plays next to a stone in the middle of the board like this:

Then there are only 3 empty points next to it. It only has 3 liberties left. If black does not try to save his stone, and white keeps playing next to it like this:

Then eventually the white stone only has one liberty left. When a stone has only one liberty left it is said to be 'in atari'. (Atari is a Japanese word which doesn't really translate well.) If black continues to ignore his stone then with one more move white can remove its last liberty. At this point the black stone is captured. White removes it from the board and keeps it, usually in the lid of the pot his stones came in. The result of the capturing move looks like this:

Question: how can a stone in the corner of the board be captured?

(Answer: as illustrated)

When there are several black stones next to each other, connected by the lines of the board, then they form a group. Groups gets captured either all at once, or not at all. For example, black has 2 groups of stones here:

One group is made up of 5 stones, and the other is made up of 3 stones. How many liberties does each group have? (Answer: The 5 stone group has 10 liberties and the 3 stone group has 8 liberties.) If black does not intervene then white can capture the 3 stone group like this:

Of course black probably does not want to have his stones captured like this. After white plays his seventh attacking move (putting the black stones in atari) black could connect his stones together by playing here:

The black stones now form a single group with 10 liberties which will be difficult for white to capture.

Eyes and the Uncapturable

You might be asking, "but are there any groups that can avoid capture indefinitely?". The answer is yes, because of the next rule of go: "You may not commit suicide". That is, you may not play a move that causes one or more of your own stones to be captured. This needs to be thought about carefully. Consider the following 2 similar situations:

The white group on the right has 1 liberty left. Black can remove it by playing in the middle which captures the white stones like this:

However the white group on the left has 10 liberties. Suppose that black tries to play in the middle of it like this:

This does not, of course, capture the white stones because they still have 9 liberties. Instead it is the black stone that have no liberties left and should be captured. This is a suicide move and is not allowed. You should compare the two moves 'black 1' in the previous 2 diagrams and make sure you understand why one is legal and the other is illegal. As a test why not try and work out which of the following black moves are legal.

(Answer: Black 1 and 2 are illegal. Black 3 and 4 are legal.)

Now that you understand the suicide rule have a look at this white group:

The white stones have 2 liberties. There are only 2 moves that might reduce the number of liberties on the white stones, but both of them are illegal. Therefore the white stones will always have at least 2 liberties and so can never be captured. An area of surrounded space like this is called an eye. The important fact is that a group with 2 eyes is alive. That is, it can never be captured. (Well, it could be captured if white played inside one of his own eyes, but that would be a rather silly thing for white to do!)

Eyes can be bigger than a single space. For example:

This white group has two big eyes and so it is alive. Black could play 3 legal moves inside it like this:

But now black cannot reduce the liberties of the black group further. Again, the white group will always have at least 2 liberties. It has 2 eyes; it is alive; black can never capture it.

On the other hand this group:

has only got 1 eye. Black may have surrounded 2 points, but they are not separate, so black could capture the white stones like this:

Whilst there are 2-eyed groups that can never be captured there are also groups that you can be sure will get captured eventually. For example consider this black group:

Whatever black does this group can never get 2 eyes. Therefore white will be able to capture it whenever he likes. (Question: how?). If there is a group like this left on the board when both players pass and the game ends then the rules say that white can just pick up the black stones off the board as prisoners.

So now you know how to capture groups of stones by surrounding them, you know how to stop your groups being captured by making 2 eyes, and you know that there are some groups that are doomed to die eventually. To familiarise yourself with the rules so far you might find it helpful to play a few games of so-called 'capture go'. Capture go is played according to the rules I have listed so far, and the winner is the first person to capture a predetermined number of stones. For example the first person to capture 3 stones, or 5 stones. Capture go is not very interesting however because (like noughts and crosses) it always ends in a draw when played well.

Territory and the End Game

I seem to have been babbling on for hours but I have not yet told you what the aim of the game is. Well, I'll tell you. The aim of the game is to make territory.

So, what is territory? You are used to the idea that groups of stones with 2 eyes can never be captured. Well, you get 1 point of territory for each empty space that that is inside one of your 2-eyed groups and you lose 1 point of territory for each one of your stones that the opponent captured during the game. For example, suppose that the game ended like this and that neither side has captured any prisoners:

In this position black and white have both made one group each and each group has exactly two eyes. The white group has surrounded 27 empty points. White has 27 points of territory. Black has surrounded 28 empty points, so black has 28 points of territory. At the end of the game the player with the most points of territory in the winner.

How do you know when you have reached the end of the game? The game ends when both players pass consecutively instead of playing a move. In the last diagram both players have played 13 stones so it must be black's turn to play next. Suppose that he decides not to pass. Then might play here:

Suppose that now both players pass. What is the score? Why don't you try counting it? You should find that both black and white have 27 points. So by playing an extra move black has thrown away his chance of winning and it is a tie. The Japanese call a tie like this 'jigo'. This points out a general principle: It is usually bad to play a move inside your own territory.

There is of course another option. Black could have played his move inside the white territory like this:

What effect does this have? You should be able to see that whatever happens this black stone can never be turned into a 2-eyed group. This stone is dead. As I explained before, if the game were to end now white could just take this stone off of the board. Now white has 1 prisoner and so black's score is (28 points on the board) - (1 prisoner held by white) = 27. White's score is still 27 and so it is jigo again - a tie. This points out another important idea. If you can't make 2 eyes then it is probably bad to play inside your opponent's territory.

There is 1 final possibility. Black could play in the larger half of white's territory like this:

In this case black might be able to make 2 eyes inside white's territory. That would destroy most of white's territory and so white will probably try and stop this. For example:

Suppose that black now realises that he can't possibly make 2 eyes here any more. What has happened to the the score? What do you think? (Answer: Black has 28 points - 3 prisoners = 25, white has 24 points, white loses by 1 point again). This illustrates a third point. If you play inside you opponent's territory in a way that threatens to live and so your opponent has to respond then it doesn't cost you anything. This means that you should feel free to have a go at invading your opponent's territory like this. On the other hand an experienced player would realise that a move like black 1 in the last diagram going to fail, and so wouldn't play it out and it would end up costing you points and possibly the game.

A 9x9 Game

I will now give a more realistic example game and show you the conventional way of counting the score at the end.

Move 30: white passes; move 31: black passes. The game is now over. The result is that black has made territory on the left side of the board and white has made territory on the right side. The one black stone inside white's territory is dead. Notice that neither white nor black have actually made groups with 2 eyes. Instead, being experienced players they know that if the opponent tries to invade they can easily make 2 eyes. This is just as good. I will now describe the usual way of counting the score. This may seem unnecessarily complicated on a small board like this, but on a 19x19 board with lots of prisoners it is much easier.

Step 1: fill in the neutral points. There is 1 empty space between the black and the white groups that does not belong to either player. It does not matter who plays these points, but they should be filled in, e.g.:

Step 2: Removing the prisoners, i.e. pick up any of your opponent's dead stones that are inside your territory.

Step 3: Fill in territory with prisoners. Your opponent loses 1 point of territory for each prisoner you have captured. The usual way to do this is to use the prisoners you have captured to fill in your opponent's territory on the board, like this:

Step 4: Rearrange the territories. Just moving stones around within the territories does not change the score and can make it easier to count. For example:

Step 5: Count up. We now count and see that black has 26 points and white has 25 points. Black has won by 1 point.

Further Rules

And those are (essentially) the whole rules of go. There are just two more rules that are needed to cover cover special cases - the ko rule which stops the game repeating and the seki rule which deals with local stalemate situations. I will tell about those next week and hope that they don't occur in any of the games you play this week. They are rather rare. If they do come up I hope that there will be a stronger player on hand to explain them to you.

I should also mention the handicapping system. When players of different abilities play, the stronger one can give the weaker one a handicap. This means that on his first move black places several stones on the board at once in a predetermined arrangement. Play then continues normally with white making the next move. For example, if I were to play one of you on a 9x9 board I would probably have to give you a 4 stone handicap. That means that on your first move you would put 4 stones onto the 4 marked points like this:

Summary

To finish, I will summarise the rules, and then you can go and try playing some games.

  1. Go is played on an square board (typically 19x19, 13x13 or 9x9) by two players who use black and white stones. Black moves first.
  2. A move consists of either a pass, or placing a stone of your colour on an empty intersection except as stated in the suicide or ko rules.
  3. (Capture rule) If, after you have played your stone, any of your opponent's groups have zero liberties then you remove the stones of these groups from the board and keep them as prisoners.
  4. (Suicide rule) If, after you have played your stone and captured any enemy pieces, any of your groups have zero liberties then your move was illegal.
  5. (The end of the game) When both players pass successively the game ends.
  6. (Scoring) When the game is over the game is scored as follows:
    • Neutral points are filled in.
    • Dead stones are removed.
    • The black and white territory is scored as points surrounded minus stones captured by the opponent.
  7. The winner is the person with the most territory.

Appendix 1: Ko

Consider the situation below:

The centre black stone is in atari. White captures with his next turn:

But now the stone White 1 is in atari himself. If Black were to recapture immediately then White do the same the same board position would repeat itself forever.

In go, the ko rule prevents this situation. It may be stated as

In a position where one stone has just been captured the player with the turn may not take back to immediately to repeat the same position.

Hence, Black may not immediately take White 1 above, instead he must play elsewhere on the board first. Black will typically play somewhere that White cannot ignore without taking an unacceptable loss of points.

(Black 2 and White 3 elsewhere on the board)

White will now play elsewhere on the board making an important move to which Black must in turn respond. If no such move important enough exists, Black may ignore White's move and connect, ending the ko:

(White 5 elsewhere on the board)

Kos play an extremely important part of the game of go and can be extremely complicated. Play where kos are taken and lost and threating moves are made elsewhere on the board are known as ko fights.

Appendix 2: Seki

Consider the situation below:

This situation is called a seki. Neither player wants to play another move in this area. Let's see why.

Firstly, it is clear that Black does not want to play:

Adding another stone costs Black a liberty and White captures all the Black stones immediately.

However, what if white plays first?

Black captures the White stones and now wherever White plays Black can make a living shape:

Neither player wants to play again so this set of stones will remain until the end of the game (presuming the white stones on the outside live).

When counting territory, this seki situation scores no points for either side. No stones are taken off and the surrounded intersections are ignored.

Sekis occur infrequently but playing inside what your opponent thought was his territory and turning it into a seki can be a game winning move.



Links

Here is a list of useful and interesting links.

General Go

Cambridge Go and Other Games

University Go Clubs in the UK

A list of University Go Clubs with which the Cambridge club have semi-frequent contact and games.

Go Teaching and Discussion